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 $180.62   11.664%   $201.6875   $201.69   $201.70   $201.70  
  Purchase #2 $249.77   9.687%   $273.9652   $273.97   $273.95   $274.00  
  Purchase #3 $181.65   11.507%   $202.5525   $202.55   $202.55   $202.60  
  Purchase #4 $213.35   9.583%   $233.7953   $233.80   $233.80   $233.80  
  Purchase #5 $31.73   7.696%   $34.1719   $34.17   $34.15   $34.20  
  Purchase #6 $131.38   11.610%   $146.6332   $146.63   $146.65   $146.60  
  Purchase #7 $101.45   13.847%   $115.4978   $115.50   $115.50   $115.50  
  7 purchase totals = $1,089.95       $1,208.3034   $1,208.31   $1,208.30   $1,208.40