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 $65.90   13.802%   $74.9955   $75.00   $75.00   $75.00  
  Purchase #2 $7.88   3.726%   $8.1736   $8.17   $8.15   $8.20  
  Purchase #3 $53.25   11.302%   $59.2683   $59.27   $59.25   $59.30  
  Purchase #4 $69.64   13.758%   $79.2211   $79.22   $79.20   $79.20  
  Purchase #5 $191.72   6.413%   $204.015   $204.02   $204.00   $204.00  
  Purchase #6 $206.53   8.576%   $224.242   $224.24   $224.25   $224.20  
  Purchase #7 $211.58   3.305%   $218.5727   $218.57   $218.55   $218.60  
  7 purchase totals = $806.50       $868.4882   $868.49   $868.40   $868.50