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 $205.77   10.169%   $226.6948   $226.69   $226.70   $226.70  
  Purchase #2 $11.82   9.427%   $12.9343   $12.93   $12.95   $12.90  
  Purchase #3 $58.85   10.143%   $64.8192   $64.82   $64.80   $64.80  
  Purchase #4 $232.58   3.511%   $240.7459   $240.75   $240.75   $240.70  
  Purchase #5 $34.92   4.745%   $36.577   $36.58   $36.60   $36.60  
  Purchase #6 $9.72   5.722%   $10.2762   $10.28   $10.30   $10.30  
  Purchase #7 $101.46   7.209%   $108.7743   $108.77   $108.75   $108.80  
  7 purchase totals = $655.12       $700.8217   $700.82   $700.85   $700.80