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 $178.94   13.421%   $202.9555   $202.96   $202.95   $203.00  
  Purchase #2 $62.80   3.420%   $64.9478   $64.95   $64.95   $64.90  
  Purchase #3 $51.43   10.695%   $56.9304   $56.93   $56.95   $56.90  
  Purchase #4 $177.80   12.837%   $200.6242   $200.62   $200.60   $200.60  
  Purchase #5 $7.98   7.722%   $8.5962   $8.60   $8.60   $8.60  
  Purchase #6 $118.44   6.812%   $126.5081   $126.51   $126.50   $126.50  
  Purchase #7 $55.60   13.649%   $63.1888   $63.19   $63.20   $63.20  
  7 purchase totals = $652.99       $723.7510   $723.76   $723.75   $723.70