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 $55.66   8.141%   $60.1913   $60.19   $60.20   $60.20  
  Purchase #2 $52.44   7.145%   $56.1868   $56.19   $56.20   $56.20  
  Purchase #3 $231.82   10.245%   $255.57   $255.57   $255.55   $255.60  
  Purchase #4 $26.63   3.499%   $27.5618   $27.56   $27.55   $27.60  
  Purchase #5 $112.25   7.643%   $120.8293   $120.83   $120.85   $120.80  
  Purchase #6 $238.55   6.760%   $254.676   $254.68   $254.70   $254.70  
  Purchase #7 $161.44   5.110%   $169.6896   $169.69   $169.70   $169.70  
  7 purchase totals = $878.79       $944.7048   $944.71   $944.75   $944.80