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 $229.60   13.659%   $260.9611   $260.96   $260.95   $261.00  
  Purchase #2 $237.77   10.316%   $262.2984   $262.30   $262.30   $262.30  
  Purchase #3 $224.26   8.691%   $243.7504   $243.75   $243.75   $243.80  
  Purchase #4 $5.34   9.344%   $5.839   $5.84   $5.85   $5.80  
  Purchase #5 $59.30   9.848%   $65.1399   $65.14   $65.15   $65.10  
  Purchase #6 $197.46   4.868%   $207.0724   $207.07   $207.05   $207.10  
  Purchase #7 $67.47   11.187%   $75.0179   $75.02   $75.00   $75.00  
  7 purchase totals = $1,021.20       $1,120.0791   $1,120.08   $1,120.05   $1,120.10