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 $157.49   9.768%   $172.8736   $172.87   $172.85   $172.90  
  Purchase #2 $136.26   8.712%   $148.131   $148.13   $148.15   $148.10  
  Purchase #3 $229.41   4.857%   $240.5524   $240.55   $240.55   $240.60  
  Purchase #4 $79.57   3.303%   $82.1982   $82.20   $82.20   $82.20  
  Purchase #5 $74.30   10.130%   $81.8266   $81.83   $81.85   $81.80  
  Purchase #6 $215.77   11.813%   $241.2589   $241.26   $241.25   $241.30  
  Purchase #7 $116.81   4.315%   $121.8504   $121.85   $121.85   $121.90  
  7 purchase totals = $1,009.61       $1,088.6911   $1,088.69   $1,088.70   $1,088.80