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 $85.88   12.141%   $96.3067   $96.31   $96.30   $96.30  
  Purchase #2 $142.61   8.133%   $154.2085   $154.21   $154.20   $154.20  
  Purchase #3 $224.56   12.370%   $252.3381   $252.34   $252.35   $252.30  
  Purchase #4 $70.74   8.769%   $76.9432   $76.94   $76.95   $76.90  
  Purchase #5 $83.61   4.527%   $87.395   $87.40   $87.40   $87.40  
  Purchase #6 $189.62   9.150%   $206.9702   $206.97   $206.95   $207.00  
  Purchase #7 $212.38   13.306%   $240.6393   $240.64   $240.65   $240.60  
  7 purchase totals = $1,009.40       $1,114.8010   $1,114.81   $1,114.80   $1,114.70