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 $85.54   9.861%   $93.9751   $93.98   $94.00   $94.00  
  Purchase #2 $18.46   11.293%   $20.5447   $20.54   $20.55   $20.50  
  Purchase #3 $39.26   13.281%   $44.4741   $44.47   $44.45   $44.50  
  Purchase #4 $225.54   6.344%   $239.8483   $239.85   $239.85   $239.80  
  Purchase #5 $198.70   9.511%   $217.5984   $217.60   $217.60   $217.60  
  Purchase #6 $95.79   3.308%   $98.9587   $98.96   $98.95   $99.00  
  Purchase #7 $48.37   7.467%   $51.9818   $51.98   $52.00   $52.00  
  7 purchase totals = $711.66       $767.3811   $767.38   $767.40   $767.40