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 $232.87   12.613%   $262.2419   $262.24   $262.25   $262.20  
  Purchase #2 $45.45   6.356%   $48.3388   $48.34   $48.35   $48.30  
  Purchase #3 $102.38   9.203%   $111.802   $111.80   $111.80   $111.80  
  Purchase #4 $156.36   5.237%   $164.5486   $164.55   $164.55   $164.50  
  Purchase #5 $226.54   12.496%   $254.8484   $254.85   $254.85   $254.80  
  Purchase #6 $50.37   5.357%   $53.0683   $53.07   $53.05   $53.10  
  Purchase #7 $9.67   6.214%   $10.2709   $10.27   $10.25   $10.30  
  7 purchase totals = $823.64       $905.1189   $905.12   $905.10   $905.00