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 $45.30   4.682%   $47.4209   $47.42   $47.40   $47.40  
  Purchase #2 $167.91   6.132%   $178.2062   $178.21   $178.20   $178.20  
  Purchase #3 $230.72   13.449%   $261.7495   $261.75   $261.75   $261.70  
  Purchase #4 $177.55   5.638%   $187.5603   $187.56   $187.55   $187.60  
  Purchase #5 $15.81   12.112%   $17.7249   $17.72   $17.70   $17.70  
  Purchase #6 $203.85   3.605%   $211.1988   $211.20   $211.20   $211.20  
  Purchase #7 $244.32   11.694%   $272.8908   $272.89   $272.90   $272.90  
  7 purchase totals = $1,085.46       $1,176.7514   $1,176.75   $1,176.70   $1,176.70