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 $248.92   13.298%   $282.0214   $282.02   $282.00   $282.00  
  Purchase #2 $91.41   6.311%   $97.1789   $97.18   $97.20   $97.20  
  Purchase #3 $140.74   6.631%   $150.0725   $150.07   $150.05   $150.10  
  Purchase #4 $51.63   5.328%   $54.3808   $54.38   $54.40   $54.40  
  Purchase #5 $164.94   3.320%   $170.416   $170.42   $170.40   $170.40  
  Purchase #6 $186.48   12.719%   $210.1984   $210.20   $210.20   $210.20  
  Purchase #7 $189.70   10.851%   $210.2843   $210.28   $210.30   $210.30  
  7 purchase totals = $1,073.82       $1,174.5523   $1,174.55   $1,174.55   $1,174.60