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 $84.83   4.143%   $88.3445   $88.34   $88.35   $88.30  
  Purchase #2 $129.77   10.172%   $142.9702   $142.97   $142.95   $143.00  
  Purchase #3 $152.99   11.116%   $169.9964   $170.00   $170.00   $170.00  
  Purchase #4 $245.47   11.834%   $274.5189   $274.52   $274.50   $274.50  
  Purchase #5 $191.78   13.686%   $218.027   $218.03   $218.05   $218.00  
  Purchase #6 $233.83   9.739%   $256.6027   $256.60   $256.60   $256.60  
  Purchase #7 $197.82   3.825%   $205.3866   $205.39   $205.40   $205.40  
  7 purchase totals = $1,236.49       $1,355.8463   $1,355.85   $1,355.85   $1,355.80