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 $68.52   9.529%   $75.0493   $75.05   $75.05   $75.00  
  Purchase #2 $216.26   12.218%   $242.6826   $242.68   $242.70   $242.70  
  Purchase #3 $161.37   12.470%   $181.4928   $181.49   $181.50   $181.50  
  Purchase #4 $85.32   8.229%   $92.341   $92.34   $92.35   $92.30  
  Purchase #5 $25.55   10.458%   $28.222   $28.22   $28.20   $28.20  
  Purchase #6 $111.63   4.693%   $116.8688   $116.87   $116.85   $116.90  
  Purchase #7 $51.25   8.184%   $55.4443   $55.44   $55.45   $55.40  
  7 purchase totals = $719.90       $792.1008   $792.09   $792.10   $792.00