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 $84.92   13.357%   $96.2628   $96.26   $96.25   $96.30  
  Purchase #2 $22.46   13.512%   $25.4948   $25.49   $25.50   $25.50  
  Purchase #3 $98.66   13.357%   $111.838   $111.84   $111.85   $111.80  
  Purchase #4 $199.55   12.226%   $223.947   $223.95   $223.95   $223.90  
  Purchase #5 $218.33   9.349%   $238.7417   $238.74   $238.75   $238.70  
  Purchase #6 $149.63   3.154%   $154.3493   $154.35   $154.35   $154.30  
  Purchase #7 $195.97   10.508%   $216.5625   $216.56   $216.55   $216.60  
  7 purchase totals = $969.52       $1,067.1961   $1,067.19   $1,067.20   $1,067.10