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 $58.62   13.559%   $66.5683   $66.57   $66.55   $66.60  
  Purchase #2 $170.44   8.675%   $185.2257   $185.23   $185.25   $185.20  
  Purchase #3 $115.55   3.470%   $119.5596   $119.56   $119.55   $119.60  
  Purchase #4 $157.89   6.571%   $168.265   $168.27   $168.25   $168.30  
  Purchase #5 $100.52   6.856%   $107.4117   $107.41   $107.40   $107.40  
  Purchase #6 $125.75   10.247%   $138.6356   $138.64   $138.65   $138.60  
  Purchase #7 $225.36   7.277%   $241.7594   $241.76   $241.75   $241.80  
  7 purchase totals = $954.13       $1,027.4253   $1,027.44   $1,027.40   $1,027.50