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 $244.56   12.259%   $274.5406   $274.54   $274.55   $274.50  
  Purchase #2 $93.95   3.872%   $97.5877   $97.59   $97.60   $97.60  
  Purchase #3 $84.55   13.572%   $96.0251   $96.03   $96.05   $96.00  
  Purchase #4 $205.30   13.412%   $232.8348   $232.83   $232.85   $232.80  
  Purchase #5 $135.73   9.778%   $149.0017   $149.00   $149.00   $149.00  
  Purchase #6 $101.40   5.801%   $107.2822   $107.28   $107.30   $107.30  
  Purchase #7 $185.69   9.711%   $203.7224   $203.72   $203.70   $203.70  
  7 purchase totals = $1,051.18       $1,160.9945   $1,160.99   $1,161.05   $1,160.90