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 $250.97   10.756%   $277.9643   $277.96   $277.95   $278.00  
  Purchase #2 $79.58   7.707%   $85.7132   $85.71   $85.70   $85.70  
  Purchase #3 $9.93   5.188%   $10.4452   $10.45   $10.45   $10.40  
  Purchase #4 $246.32   13.360%   $279.2284   $279.23   $279.25   $279.20  
  Purchase #5 $179.44   9.834%   $197.0861   $197.09   $197.10   $197.10  
  Purchase #6 $118.81   5.717%   $125.6024   $125.60   $125.60   $125.60  
  Purchase #7 $157.84   12.612%   $177.7468   $177.75   $177.75   $177.70  
  7 purchase totals = $1,042.89       $1,153.7864   $1,153.79   $1,153.80   $1,153.70