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 $209.41   10.416%   $231.2221   $231.22   $231.20   $231.20  
  Purchase #2 $83.97   12.297%   $94.2958   $94.30   $94.30   $94.30  
  Purchase #3 $189.70   3.308%   $195.9753   $195.98   $196.00   $196.00  
  Purchase #4 $245.33   13.228%   $277.7823   $277.78   $277.80   $277.80  
  Purchase #5 $193.56   6.665%   $206.4608   $206.46   $206.45   $206.50  
  Purchase #6 $241.36   10.291%   $266.1984   $266.20   $266.20   $266.20  
  Purchase #7 $130.94   7.325%   $140.5314   $140.53   $140.55   $140.50  
  7 purchase totals = $1,294.27       $1,412.4661   $1,412.47   $1,412.50   $1,412.50