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 $76.68   8.204%   $82.9708   $82.97   $82.95   $83.00  
  Purchase #2 $109.89   11.782%   $122.8372   $122.84   $122.85   $122.80  
  Purchase #3 $199.46   13.297%   $225.9822   $225.98   $226.00   $226.00  
  Purchase #4 $15.55   6.670%   $16.5872   $16.59   $16.60   $16.60  
  Purchase #5 $14.46   4.337%   $15.0871   $15.09   $15.10   $15.10  
  Purchase #6 $195.49   13.107%   $221.1129   $221.11   $221.10   $221.10  
  Purchase #7 $189.82   13.121%   $214.7263   $214.73   $214.75   $214.70  
  7 purchase totals = $801.35       $899.3037   $899.31   $899.35   $899.30