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 $205.32   4.770%   $215.1138   $215.11   $215.10   $215.10  
  Purchase #2 $243.61   12.211%   $273.3572   $273.36   $273.35   $273.40  
  Purchase #3 $32.75   4.156%   $34.1111   $34.11   $34.10   $34.10  
  Purchase #4 $26.28   11.587%   $29.3251   $29.33   $29.35   $29.30  
  Purchase #5 $169.56   11.177%   $188.5117   $188.51   $188.50   $188.50  
  Purchase #6 $170.60   4.358%   $178.0347   $178.03   $178.05   $178.00  
  Purchase #7 $20.96   8.328%   $22.7055   $22.71   $22.70   $22.70  
  7 purchase totals = $869.08       $941.1591   $941.16   $941.15   $941.10