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 $75.63   11.746%   $84.5135   $84.51   $84.50   $84.50  
  Purchase #2 $207.78   5.711%   $219.6463   $219.65   $219.65   $219.60  
  Purchase #3 $77.79   8.365%   $84.2971   $84.30   $84.30   $84.30  
  Purchase #4 $241.74   13.563%   $274.5272   $274.53   $274.55   $274.50  
  Purchase #5 $118.53   6.748%   $126.5284   $126.53   $126.55   $126.50  
  Purchase #6 $166.77   7.344%   $179.0176   $179.02   $179.00   $179.00  
  Purchase #7 $91.44   6.774%   $97.6341   $97.63   $97.65   $97.60  
  7 purchase totals = $979.68       $1,066.1642   $1,066.17   $1,066.20   $1,066.00