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 $52.91   3.237%   $54.6227   $54.62   $54.60   $54.60  
  Purchase #2 $148.57   10.296%   $163.8668   $163.87   $163.85   $163.90  
  Purchase #3 $137.55   11.667%   $153.598   $153.60   $153.60   $153.60  
  Purchase #4 $242.35   10.746%   $268.3929   $268.39   $268.40   $268.40  
  Purchase #5 $79.66   11.754%   $89.0232   $89.02   $89.00   $89.00  
  Purchase #6 $141.47   8.206%   $153.079   $153.08   $153.10   $153.10  
  Purchase #7 $33.93   13.215%   $38.4138   $38.41   $38.40   $38.40  
  7 purchase totals = $836.44       $920.9964   $920.99   $920.95   $921.00