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 $214.84   10.304%   $236.9771   $236.98   $237.00   $237.00  
  Purchase #2 $13.82   6.287%   $14.6889   $14.69   $14.70   $14.70  
  Purchase #3 $112.38   4.859%   $117.8405   $117.84   $117.85   $117.80  
  Purchase #4 $91.66   6.530%   $97.6454   $97.65   $97.65   $97.60  
  Purchase #5 $241.97   11.873%   $270.6991   $270.70   $270.70   $270.70  
  Purchase #6 $209.41   9.844%   $230.0243   $230.02   $230.00   $230.00  
  Purchase #7 $197.74   8.276%   $214.105   $214.11   $214.10   $214.10  
  7 purchase totals = $1,081.82       $1,181.9803   $1,181.99   $1,182.00   $1,181.90