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 $66.95   11.613%   $74.7249   $74.72   $74.70   $74.70  
  Purchase #2 $228.50   12.691%   $257.4989   $257.50   $257.50   $257.50  
  Purchase #3 $65.97   8.179%   $71.3657   $71.37   $71.35   $71.40  
  Purchase #4 $202.87   12.332%   $227.8879   $227.89   $227.90   $227.90  
  Purchase #5 $123.80   7.749%   $133.3933   $133.39   $133.40   $133.40  
  Purchase #6 $156.93   5.849%   $166.1088   $166.11   $166.10   $166.10  
  Purchase #7 $86.59   12.479%   $97.3956   $97.40   $97.40   $97.40  
  7 purchase totals = $931.61       $1,028.3751   $1,028.38   $1,028.35   $1,028.40