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 $46.94   8.724%   $51.035   $51.04   $51.05   $51.00  
  Purchase #2 $221.73   11.349%   $246.8941   $246.89   $246.90   $246.90  
  Purchase #3 $173.81   10.768%   $192.5259   $192.53   $192.55   $192.50  
  Purchase #4 $118.68   12.139%   $133.0866   $133.09   $133.10   $133.10  
  Purchase #5 $238.99   5.159%   $251.3195   $251.32   $251.30   $251.30  
  Purchase #6 $94.43   11.106%   $104.9174   $104.92   $104.90   $104.90  
  Purchase #7 $169.74   3.865%   $176.3005   $176.30   $176.30   $176.30  
  7 purchase totals = $1,064.32       $1,156.0790   $1,156.09   $1,156.10   $1,156.00