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 $53.43   8.864%   $58.166   $58.17   $58.15   $58.20  
  Purchase #2 $219.52   5.707%   $232.048   $232.05   $232.05   $232.00  
  Purchase #3 $187.77   4.576%   $196.3624   $196.36   $196.35   $196.40  
  Purchase #4 $119.91   7.592%   $129.0136   $129.01   $129.00   $129.00  
  Purchase #5 $64.77   9.844%   $71.146   $71.15   $71.15   $71.10  
  Purchase #6 $246.40   10.451%   $272.1513   $272.15   $272.15   $272.20  
  Purchase #7 $20.54   9.480%   $22.4872   $22.49   $22.50   $22.50  
  7 purchase totals = $912.34       $981.3745   $981.38   $981.35   $981.40