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 $49.59   10.225%   $54.6606   $54.66   $54.65   $54.70  
  Purchase #2 $227.76   11.269%   $253.4263   $253.43   $253.45   $253.40  
  Purchase #3 $168.75   8.348%   $182.8373   $182.84   $182.85   $182.80  
  Purchase #4 $245.91   11.423%   $274.0003   $274.00   $274.00   $274.00  
  Purchase #5 $141.29   6.523%   $150.5063   $150.51   $150.50   $150.50  
  Purchase #6 $192.37   8.874%   $209.4409   $209.44   $209.45   $209.40  
  Purchase #7 $194.84   3.872%   $202.3842   $202.38   $202.40   $202.40  
  7 purchase totals = $1,220.51       $1,327.2559   $1,327.26   $1,327.30   $1,327.20