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 $192.48   8.683%   $209.193   $209.19   $209.20   $209.20  
  Purchase #2 $57.79   4.656%   $60.4807   $60.48   $60.50   $60.50  
  Purchase #3 $71.44   6.263%   $75.9143   $75.91   $75.90   $75.90  
  Purchase #4 $149.67   6.433%   $159.2983   $159.30   $159.30   $159.30  
  Purchase #5 $27.88   7.110%   $29.8623   $29.86   $29.85   $29.90  
  Purchase #6 $221.43   6.821%   $236.5337   $236.53   $236.55   $236.50  
  Purchase #7 $5.30   7.624%   $5.7041   $5.70   $5.70   $5.70  
  7 purchase totals = $725.99       $776.9864   $776.97   $777.00   $777.00