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 $232.72   8.613%   $252.7642   $252.76   $252.75   $252.80  
  Purchase #2 $95.87   12.394%   $107.7521   $107.75   $107.75   $107.80  
  Purchase #3 $210.71   7.578%   $226.6776   $226.68   $226.70   $226.70  
  Purchase #4 $62.29   8.597%   $67.6451   $67.65   $67.65   $67.60  
  Purchase #5 $28.93   3.826%   $30.0369   $30.04   $30.05   $30.00  
  Purchase #6 $234.66   8.550%   $254.7234   $254.72   $254.70   $254.70  
  Purchase #7 $197.98   3.708%   $205.3211   $205.32   $205.30   $205.30  
  7 purchase totals = $1,063.16       $1,144.9204   $1,144.92   $1,144.90   $1,144.90