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 $91.62   5.142%   $96.3311   $96.33   $96.35   $96.30  
  Purchase #2 $31.66   4.159%   $32.9767   $32.98   $33.00   $33.00  
  Purchase #3 $26.90   6.247%   $28.5804   $28.58   $28.60   $28.60  
  Purchase #4 $240.46   10.288%   $265.1985   $265.20   $265.20   $265.20  
  Purchase #5 $49.87   9.287%   $54.5014   $54.50   $54.50   $54.50  
  Purchase #6 $114.47   8.821%   $124.5674   $124.57   $124.55   $124.60  
  Purchase #7 $132.66   4.191%   $138.2198   $138.22   $138.20   $138.20  
  7 purchase totals = $687.64       $740.3753   $740.38   $740.40   $740.40