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 $132.57   7.138%   $142.0328   $142.03   $142.05   $142.00  
  Purchase #2 $244.95   5.409%   $258.1993   $258.20   $258.20   $258.20  
  Purchase #3 $83.47   10.763%   $92.4539   $92.45   $92.45   $92.50  
  Purchase #4 $58.94   9.470%   $64.5216   $64.52   $64.50   $64.50  
  Purchase #5 $247.68   10.687%   $274.1496   $274.15   $274.15   $274.10  
  Purchase #6 $154.57   11.856%   $172.8958   $172.90   $172.90   $172.90  
  Purchase #7 $63.75   4.320%   $66.504   $66.50   $66.50   $66.50  
  7 purchase totals = $985.93       $1,070.7570   $1,070.75   $1,070.75   $1,070.70