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 $68.32   4.713%   $71.5399   $71.54   $71.55   $71.50  
  Purchase #2 $67.43   8.222%   $72.9741   $72.97   $72.95   $73.00  
  Purchase #3 $229.60   6.190%   $243.8122   $243.81   $243.80   $243.80  
  Purchase #4 $47.37   3.439%   $48.9991   $49.00   $49.00   $49.00  
  Purchase #5 $62.36   7.355%   $66.9466   $66.95   $66.95   $66.90  
  Purchase #6 $8.84   13.634%   $10.0452   $10.05   $10.05   $10.00  
  Purchase #7 $225.39   8.693%   $244.9832   $244.98   $245.00   $245.00  
  7 purchase totals = $709.31       $759.3003   $759.30   $759.30   $759.20