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 $234.86   6.275%   $249.5975   $249.60   $249.60   $249.60  
  Purchase #2 $191.70   9.866%   $210.6131   $210.61   $210.60   $210.60  
  Purchase #3 $161.33   8.855%   $175.6158   $175.62   $175.60   $175.60  
  Purchase #4 $225.29   12.200%   $252.7754   $252.78   $252.80   $252.80  
  Purchase #5 $14.75   6.410%   $15.6955   $15.70   $15.70   $15.70  
  Purchase #6 $91.38   6.779%   $97.5747   $97.57   $97.55   $97.60  
  Purchase #7 $47.77   10.614%   $52.8403   $52.84   $52.85   $52.80  
  7 purchase totals = $967.08       $1,054.7123   $1,054.72   $1,054.70   $1,054.70