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 $93.75   10.584%   $103.6725   $103.67   $103.65   $103.70  
  Purchase #2 $238.94   10.218%   $263.3549   $263.35   $263.35   $263.40  
  Purchase #3 $161.76   9.271%   $176.7568   $176.76   $176.75   $176.80  
  Purchase #4 $58.97   12.773%   $66.5022   $66.50   $66.50   $66.50  
  Purchase #5 $240.43   6.350%   $255.6973   $255.70   $255.70   $255.70  
  Purchase #6 $103.70   5.294%   $109.1899   $109.19   $109.20   $109.20  
  Purchase #7 $64.47   6.448%   $68.627   $68.63   $68.65   $68.60  
  7 purchase totals = $962.02       $1,043.8006   $1,043.80   $1,043.80   $1,043.90