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 $55.99   10.376%   $61.7995   $61.80   $61.80   $61.80  
  Purchase #2 $11.97   10.658%   $13.2458   $13.25   $13.25   $13.20  
  Purchase #3 $64.57   6.315%   $68.6476   $68.65   $68.65   $68.60  
  Purchase #4 $52.38   12.238%   $58.7903   $58.79   $58.80   $58.80  
  Purchase #5 $59.67   3.846%   $61.9649   $61.96   $61.95   $62.00  
  Purchase #6 $84.82   8.165%   $91.7456   $91.75   $91.75   $91.70  
  Purchase #7 $56.58   8.328%   $61.292   $61.29   $61.30   $61.30  
  7 purchase totals = $385.98       $417.4857   $417.49   $417.50   $417.40