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 $187.96   13.294%   $212.9474   $212.95   $212.95   $212.90  
  Purchase #2 $211.70   10.183%   $233.2574   $233.26   $233.25   $233.30  
  Purchase #3 $154.57   10.175%   $170.2975   $170.30   $170.30   $170.30  
  Purchase #4 $228.70   5.468%   $241.2053   $241.21   $241.20   $241.20  
  Purchase #5 $111.78   6.686%   $119.2536   $119.25   $119.25   $119.30  
  Purchase #6 $204.56   12.519%   $230.1689   $230.17   $230.15   $230.20  
  Purchase #7 $117.86   7.713%   $126.9505   $126.95   $126.95   $127.00  
  7 purchase totals = $1,217.13       $1,334.0806   $1,334.09   $1,334.05   $1,334.20