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 $91.35   4.112%   $95.1063   $95.11   $95.10   $95.10  
  Purchase #2 $41.45   12.343%   $46.5662   $46.57   $46.55   $46.60  
  Purchase #3 $32.85   4.143%   $34.211   $34.21   $34.20   $34.20  
  Purchase #4 $188.30   3.677%   $195.2238   $195.22   $195.20   $195.20  
  Purchase #5 $178.43   10.634%   $197.4042   $197.40   $197.40   $197.40  
  Purchase #6 $230.98   4.227%   $240.7435   $240.74   $240.75   $240.70  
  Purchase #7 $182.40   5.102%   $191.706   $191.71   $191.70   $191.70  
  7 purchase totals = $945.76       $1,000.9610   $1,000.96   $1,000.90   $1,000.90