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 $54.61   8.775%   $59.402   $59.40   $59.40   $59.40  
  Purchase #2 $141.49   13.575%   $160.6973   $160.70   $160.70   $160.70  
  Purchase #3 $50.96   11.263%   $56.6996   $56.70   $56.70   $56.70  
  Purchase #4 $231.94   12.211%   $260.2622   $260.26   $260.25   $260.30  
  Purchase #5 $55.99   9.572%   $61.3494   $61.35   $61.35   $61.30  
  Purchase #6 $52.30   6.681%   $55.7942   $55.79   $55.80   $55.80  
  Purchase #7 $162.32   12.363%   $182.3876   $182.39   $182.40   $182.40  
  7 purchase totals = $749.61       $836.5923   $836.59   $836.60   $836.60