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 $236.34   3.866%   $245.4769   $245.48   $245.50   $245.50  
  Purchase #2 $61.96   12.716%   $69.8388   $69.84   $69.85   $69.80  
  Purchase #3 $246.96   12.599%   $278.0745   $278.07   $278.05   $278.10  
  Purchase #4 $233.99   12.790%   $263.9173   $263.92   $263.90   $263.90  
  Purchase #5 $247.74   7.578%   $266.5137   $266.51   $266.50   $266.50  
  Purchase #6 $126.80   3.789%   $131.6045   $131.60   $131.60   $131.60  
  Purchase #7 $12.64   4.424%   $13.1992   $13.20   $13.20   $13.20  
  7 purchase totals = $1,166.43       $1,268.6249   $1,268.62   $1,268.60   $1,268.60