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 $47.29   6.374%   $50.3043   $50.30   $50.30   $50.30  
  Purchase #2 $166.75   11.871%   $186.5449   $186.54   $186.55   $186.50  
  Purchase #3 $195.59   3.731%   $202.8875   $202.89   $202.90   $202.90  
  Purchase #4 $232.31   8.741%   $252.6162   $252.62   $252.60   $252.60  
  Purchase #5 $107.78   11.219%   $119.8718   $119.87   $119.85   $119.90  
  Purchase #6 $12.84   13.483%   $14.5712   $14.57   $14.55   $14.60  
  Purchase #7 $168.26   9.171%   $183.6911   $183.69   $183.70   $183.70  
  7 purchase totals = $930.82       $1,010.4870   $1,010.48   $1,010.45   $1,010.50