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 $72.84   12.534%   $81.9698   $81.97   $81.95   $82.00  
  Purchase #2 $195.63   4.560%   $204.5507   $204.55   $204.55   $204.60  
  Purchase #3 $162.64   5.787%   $172.052   $172.05   $172.05   $172.10  
  Purchase #4 $85.27   3.472%   $88.2306   $88.23   $88.25   $88.20  
  Purchase #5 $17.98   11.840%   $20.1088   $20.11   $20.10   $20.10  
  Purchase #6 $132.59   3.278%   $136.9363   $136.94   $136.95   $136.90  
  Purchase #7 $142.71   12.693%   $160.8242   $160.82   $160.80   $160.80  
  7 purchase totals = $809.66       $864.6724   $864.67   $864.65   $864.70