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 $128.77   7.450%   $138.3634   $138.36   $138.35   $138.40  
  Purchase #2 $105.39   5.821%   $111.5248   $111.52   $111.50   $111.50  
  Purchase #3 $210.68   8.843%   $229.3104   $229.31   $229.30   $229.30  
  Purchase #4 $69.56   6.711%   $74.2282   $74.23   $74.25   $74.20  
  Purchase #5 $74.50   5.633%   $78.6966   $78.70   $78.70   $78.70  
  Purchase #6 $55.92   13.696%   $63.5788   $63.58   $63.60   $63.60  
  Purchase #7 $29.40   11.272%   $32.714   $32.71   $32.70   $32.70  
  7 purchase totals = $674.22       $728.4162   $728.41   $728.40   $728.40