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 $84.62   9.363%   $92.543   $92.54   $92.55   $92.50  
  Purchase #2 $222.72   10.817%   $246.8116   $246.81   $246.80   $246.80  
  Purchase #3 $24.76   10.376%   $27.3291   $27.33   $27.35   $27.30  
  Purchase #4 $60.34   10.162%   $66.4718   $66.47   $66.45   $66.50  
  Purchase #5 $156.51   11.159%   $173.975   $173.98   $174.00   $174.00  
  Purchase #6 $120.27   13.556%   $136.5738   $136.57   $136.55   $136.60  
  Purchase #7 $162.47   6.586%   $173.1703   $173.17   $173.15   $173.20  
  7 purchase totals = $831.69       $916.8746   $916.87   $916.85   $916.90