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 $235.91   13.232%   $267.1256   $267.13   $267.15   $267.10  
  Purchase #2 $72.73   6.224%   $77.2567   $77.26   $77.25   $77.30  
  Purchase #3 $84.87   7.458%   $91.1996   $91.20   $91.20   $91.20  
  Purchase #4 $187.66   10.843%   $208.008   $208.01   $208.00   $208.00  
  Purchase #5 $110.60   4.475%   $115.5494   $115.55   $115.55   $115.50  
  Purchase #6 $83.97   4.588%   $87.8225   $87.82   $87.80   $87.80  
  Purchase #7 $101.45   5.817%   $107.3513   $107.35   $107.35   $107.40  
  7 purchase totals = $877.19       $954.3131   $954.32   $954.30   $954.30