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 $73.58   10.420%   $81.247   $81.25   $81.25   $81.20  
  Purchase #2 $202.29   12.543%   $227.6632   $227.66   $227.65   $227.70  
  Purchase #3 $47.51   11.176%   $52.8197   $52.82   $52.80   $52.80  
  Purchase #4 $218.62   5.114%   $229.8002   $229.80   $229.80   $229.80  
  Purchase #5 $162.44   9.809%   $178.3737   $178.37   $178.35   $178.40  
  Purchase #6 $113.57   3.380%   $117.4087   $117.41   $117.40   $117.40  
  Purchase #7 $111.48   8.862%   $121.3594   $121.36   $121.35   $121.40  
  7 purchase totals = $929.49       $1,008.6719   $1,008.67   $1,008.60   $1,008.70