Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $129.82   5.738%   $137.2691   $137.27   $137.25   $137.30  
  Purchase #2 $205.84   6.835%   $219.9092   $219.91   $219.90   $219.90  
  Purchase #3 $246.26   11.406%   $274.3484   $274.35   $274.35   $274.30  
  Purchase #4 $138.52   5.655%   $146.3533   $146.35   $146.35   $146.40  
  Purchase #5 $156.93   6.540%   $167.1932   $167.19   $167.20   $167.20  
  Purchase #6 $235.99   10.722%   $261.2928   $261.29   $261.30   $261.30  
  Purchase #7 $200.81   13.414%   $227.7467   $227.75   $227.75   $227.70  
  7 purchase totals = $1,314.17       $1,434.1127   $1,434.11   $1,434.10   $1,434.10