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 $190.31   6.339%   $202.3738   $202.37   $202.35   $202.40  
  Purchase #2 $215.87   10.334%   $238.178   $238.18   $238.20   $238.20  
  Purchase #3 $73.95   3.563%   $76.5848   $76.58   $76.60   $76.60  
  Purchase #4 $160.46   5.728%   $169.6511   $169.65   $169.65   $169.70  
  Purchase #5 $244.97   4.474%   $255.93   $255.93   $255.95   $255.90  
  Purchase #6 $83.28   11.252%   $92.6507   $92.65   $92.65   $92.70  
  Purchase #7 $183.38   8.366%   $198.7216   $198.72   $198.70   $198.70  
  7 purchase totals = $1,152.22       $1,234.0900   $1,234.08   $1,234.10   $1,234.20