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 $57.55   4.344%   $60.05   $60.05   $60.05   $60.10  
  Purchase #2 $147.63   11.804%   $165.0562   $165.06   $165.05   $165.10  
  Purchase #3 $57.31   7.757%   $61.7555   $61.76   $61.75   $61.80  
  Purchase #4 $59.93   10.305%   $66.1058   $66.11   $66.10   $66.10  
  Purchase #5 $236.75   6.615%   $252.411   $252.41   $252.40   $252.40  
  Purchase #6 $59.69   12.746%   $67.2981   $67.30   $67.30   $67.30  
  Purchase #7 $104.81   5.271%   $110.3345   $110.33   $110.35   $110.30  
  7 purchase totals = $723.67       $783.0111   $783.02   $783.00   $783.10