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 $87.82   6.599%   $93.6152   $93.62   $93.60   $93.60  
  Purchase #2 $25.67   13.516%   $29.1396   $29.14   $29.15   $29.10  
  Purchase #3 $250.77   5.825%   $265.3774   $265.38   $265.40   $265.40  
  Purchase #4 $146.57   10.207%   $161.5304   $161.53   $161.55   $161.50  
  Purchase #5 $180.77   10.328%   $199.4399   $199.44   $199.45   $199.40  
  Purchase #6 $138.90   11.664%   $155.1013   $155.10   $155.10   $155.10  
  Purchase #7 $80.78   11.827%   $90.3339   $90.33   $90.35   $90.30  
  7 purchase totals = $911.28       $994.5377   $994.54   $994.60   $994.40