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 $209.39   8.298%   $226.7652   $226.77   $226.75   $226.80  
  Purchase #2 $197.89   6.581%   $210.9131   $210.91   $210.90   $210.90  
  Purchase #3 $30.77   8.859%   $33.4959   $33.50   $33.50   $33.50  
  Purchase #4 $171.74   13.402%   $194.7566   $194.76   $194.75   $194.80  
  Purchase #5 $182.34   9.744%   $200.1072   $200.11   $200.10   $200.10  
  Purchase #6 $59.44   13.255%   $67.3188   $67.32   $67.30   $67.30  
  Purchase #7 $166.64   4.512%   $174.1588   $174.16   $174.15   $174.20  
  7 purchase totals = $1,018.21       $1,107.5156   $1,107.53   $1,107.45   $1,107.60