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 $66.50   11.346%   $74.0451   $74.05   $74.05   $74.00  
  Purchase #2 $227.72   4.721%   $238.4707   $238.47   $238.45   $238.50  
  Purchase #3 $163.51   6.827%   $174.6728   $174.67   $174.65   $174.70  
  Purchase #4 $7.97   6.179%   $8.4625   $8.46   $8.45   $8.50  
  Purchase #5 $199.82   5.733%   $211.2757   $211.28   $211.30   $211.30  
  Purchase #6 $13.36   11.327%   $14.8733   $14.87   $14.85   $14.90  
  Purchase #7 $228.30   7.348%   $245.0755   $245.08   $245.10   $245.10  
  7 purchase totals = $907.18       $966.8756   $966.88   $966.85   $967.00