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 $12.95   12.279%   $14.5401   $14.54   $14.55   $14.50  
  Purchase #2 $201.60   3.825%   $209.3112   $209.31   $209.30   $209.30  
  Purchase #3 $58.48   10.578%   $64.666   $64.67   $64.65   $64.70  
  Purchase #4 $32.70   5.494%   $34.4965   $34.50   $34.50   $34.50  
  Purchase #5 $123.76   5.773%   $130.9047   $130.90   $130.90   $130.90  
  Purchase #6 $240.64   3.320%   $248.6292   $248.63   $248.65   $248.60  
  Purchase #7 $233.29   9.871%   $256.3181   $256.32   $256.30   $256.30  
  7 purchase totals = $903.42       $958.8658   $958.87   $958.85   $958.80