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 $212.98   12.352%   $239.2873   $239.29   $239.30   $239.30  
  Purchase #2 $198.95   5.681%   $210.2523   $210.25   $210.25   $210.30  
  Purchase #3 $235.87   10.548%   $260.7496   $260.75   $260.75   $260.70  
  Purchase #4 $172.44   6.185%   $183.1054   $183.11   $183.10   $183.10  
  Purchase #5 $57.94   12.697%   $65.2966   $65.30   $65.30   $65.30  
  Purchase #6 $212.99   9.287%   $232.7704   $232.77   $232.75   $232.80  
  Purchase #7 $158.78   10.586%   $175.5885   $175.59   $175.60   $175.60  
  7 purchase totals = $1,249.95       $1,367.0501   $1,367.06   $1,367.05   $1,367.10