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 $194.48   6.271%   $206.6758   $206.68   $206.70   $206.70  
  Purchase #2 $98.63   4.640%   $103.2064   $103.21   $103.20   $103.20  
  Purchase #3 $249.38   8.874%   $271.51   $271.51   $271.50   $271.50  
  Purchase #4 $224.37   7.195%   $240.5134   $240.51   $240.50   $240.50  
  Purchase #5 $197.76   7.478%   $212.5485   $212.55   $212.55   $212.50  
  Purchase #6 $210.57   11.119%   $233.9833   $233.98   $234.00   $234.00  
  Purchase #7 $127.56   8.453%   $138.3426   $138.34   $138.35   $138.30  
  7 purchase totals = $1,302.75       $1,406.7800   $1,406.78   $1,406.80   $1,406.70