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 $196.77   3.731%   $204.1115   $204.11   $204.10   $204.10  
  Purchase #2 $152.48   9.280%   $166.6301   $166.63   $166.65   $166.60  
  Purchase #3 $17.53   9.112%   $19.1273   $19.13   $19.15   $19.10  
  Purchase #4 $192.26   10.631%   $212.6992   $212.70   $212.70   $212.70  
  Purchase #5 $174.91   13.814%   $199.0721   $199.07   $199.05   $199.10  
  Purchase #6 $14.96   8.544%   $16.2382   $16.24   $16.25   $16.20  
  Purchase #7 $134.53   12.705%   $151.622   $151.62   $151.60   $151.60  
  7 purchase totals = $883.44       $969.5004   $969.50   $969.50   $969.40