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 $205.41   13.656%   $233.4608   $233.46   $233.45   $233.50  
  Purchase #2 $41.97   11.177%   $46.661   $46.66   $46.65   $46.70  
  Purchase #3 $248.95   12.402%   $279.8248   $279.82   $279.80   $279.80  
  Purchase #4 $55.42   9.725%   $60.8096   $60.81   $60.80   $60.80  
  Purchase #5 $168.67   11.112%   $187.4126   $187.41   $187.40   $187.40  
  Purchase #6 $179.46   12.156%   $201.2752   $201.28   $201.30   $201.30  
  Purchase #7 $83.40   13.516%   $94.6723   $94.67   $94.65   $94.70  
  7 purchase totals = $983.28       $1,104.1163   $1,104.11   $1,104.05   $1,104.20