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 $54.62   4.842%   $57.2647   $57.26   $57.25   $57.30  
  Purchase #2 $232.86   9.795%   $255.6686   $255.67   $255.65   $255.70  
  Purchase #3 $241.82   10.834%   $268.0188   $268.02   $268.00   $268.00  
  Purchase #4 $207.26   7.149%   $222.077   $222.08   $222.10   $222.10  
  Purchase #5 $243.54   13.289%   $275.904   $275.90   $275.90   $275.90  
  Purchase #6 $221.45   11.209%   $246.2723   $246.27   $246.25   $246.30  
  Purchase #7 $16.68   10.133%   $18.3702   $18.37   $18.35   $18.40  
  7 purchase totals = $1,218.23       $1,343.5756   $1,343.57   $1,343.50   $1,343.70