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 $185.73   9.794%   $203.9204   $203.92   $203.90   $203.90  
  Purchase #2 $233.25   11.568%   $260.2324   $260.23   $260.25   $260.20  
  Purchase #3 $181.64   10.806%   $201.268   $201.27   $201.25   $201.30  
  Purchase #4 $176.34   13.704%   $200.5056   $200.51   $200.50   $200.50  
  Purchase #5 $37.42   9.461%   $40.9603   $40.96   $40.95   $41.00  
  Purchase #6 $97.53   5.627%   $103.018   $103.02   $103.00   $103.00  
  Purchase #7 $201.66   5.693%   $213.1405   $213.14   $213.15   $213.10  
  7 purchase totals = $1,113.57       $1,223.0452   $1,223.05   $1,223.00   $1,223.00