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 $97.53   11.506%   $108.7518   $108.75   $108.75   $108.80  
  Purchase #2 $231.49   10.418%   $255.6066   $255.61   $255.60   $255.60  
  Purchase #3 $219.99   3.137%   $226.8911   $226.89   $226.90   $226.90  
  Purchase #4 $8.53   11.834%   $9.5394   $9.54   $9.55   $9.50  
  Purchase #5 $151.36   5.871%   $160.2463   $160.25   $160.25   $160.20  
  Purchase #6 $174.41   3.625%   $180.7324   $180.73   $180.75   $180.70  
  Purchase #7 $102.82   11.395%   $114.5363   $114.54   $114.55   $114.50  
  7 purchase totals = $986.13       $1,056.3039   $1,056.31   $1,056.35   $1,056.20