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 $213.91   7.104%   $229.1062   $229.11   $229.10   $229.10  
  Purchase #2 $49.86   13.269%   $56.4759   $56.48   $56.50   $56.50  
  Purchase #3 $8.97   7.564%   $9.6485   $9.65   $9.65   $9.60  
  Purchase #4 $211.28   5.674%   $223.268   $223.27   $223.25   $223.30  
  Purchase #5 $109.65   7.420%   $117.786   $117.79   $117.80   $117.80  
  Purchase #6 $250.87   10.131%   $276.2856   $276.29   $276.30   $276.30  
  Purchase #7 $144.73   13.201%   $163.8358   $163.84   $163.85   $163.80  
  7 purchase totals = $989.27       $1,076.4060   $1,076.43   $1,076.45   $1,076.40