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 $232.65   13.172%   $263.2947   $263.29   $263.30   $263.30  
  Purchase #2 $219.81   5.618%   $232.1589   $232.16   $232.15   $232.20  
  Purchase #3 $55.35   3.232%   $57.1389   $57.14   $57.15   $57.10  
  Purchase #4 $147.85   10.237%   $162.9854   $162.99   $163.00   $163.00  
  Purchase #5 $189.73   9.261%   $207.3009   $207.30   $207.30   $207.30  
  Purchase #6 $55.29   5.110%   $58.1153   $58.12   $58.10   $58.10  
  Purchase #7 $245.89   8.316%   $266.3382   $266.34   $266.35   $266.30  
  7 purchase totals = $1,146.57       $1,247.3323   $1,247.34   $1,247.35   $1,247.30