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 $245.53   3.698%   $254.6097   $254.61   $254.60   $254.60  
  Purchase #2 $152.66   8.617%   $165.8147   $165.81   $165.80   $165.80  
  Purchase #3 $126.79   9.873%   $139.308   $139.31   $139.30   $139.30  
  Purchase #4 $53.69   11.403%   $59.8123   $59.81   $59.80   $59.80  
  Purchase #5 $69.47   6.698%   $74.1231   $74.12   $74.10   $74.10  
  Purchase #6 $129.54   12.342%   $145.5278   $145.53   $145.55   $145.50  
  Purchase #7 $244.70   9.516%   $267.9857   $267.99   $268.00   $268.00  
  7 purchase totals = $1,022.38       $1,107.1813   $1,107.18   $1,107.15   $1,107.10