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 $59.36   3.829%   $61.6329   $61.63   $61.65   $61.60  
  Purchase #2 $220.93   11.450%   $246.2265   $246.23   $246.25   $246.20  
  Purchase #3 $180.44   11.614%   $201.3963   $201.40   $201.40   $201.40  
  Purchase #4 $137.29   8.516%   $148.9816   $148.98   $149.00   $149.00  
  Purchase #5 $65.49   4.297%   $68.3041   $68.30   $68.30   $68.30  
  Purchase #6 $63.48   5.786%   $67.153   $67.15   $67.15   $67.20  
  Purchase #7 $28.98   12.747%   $32.6741   $32.67   $32.65   $32.70  
  7 purchase totals = $755.97       $826.3685   $826.36   $826.40   $826.40