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 $83.58   5.321%   $88.0273   $88.03   $88.05   $88.00  
  Purchase #2 $46.79   4.282%   $48.7935   $48.79   $48.80   $48.80  
  Purchase #3 $179.89   6.409%   $191.4192   $191.42   $191.40   $191.40  
  Purchase #4 $226.66   3.558%   $234.7246   $234.72   $234.70   $234.70  
  Purchase #5 $182.80   11.596%   $203.9975   $204.00   $204.00   $204.00  
  Purchase #6 $54.34   5.632%   $57.4004   $57.40   $57.40   $57.40  
  Purchase #7 $94.35   4.598%   $98.6882   $98.69   $98.70   $98.70  
  7 purchase totals = $868.41       $923.0507   $923.05   $923.05   $923.00