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 $165.83   6.308%   $176.2906   $176.29   $176.30   $176.30  
  Purchase #2 $58.50   8.112%   $63.2455   $63.25   $63.25   $63.20  
  Purchase #3 $248.73   13.282%   $281.7663   $281.77   $281.75   $281.80  
  Purchase #4 $45.91   13.687%   $52.1937   $52.19   $52.20   $52.20  
  Purchase #5 $125.91   3.132%   $129.8535   $129.85   $129.85   $129.90  
  Purchase #6 $201.84   4.696%   $211.3184   $211.32   $211.30   $211.30  
  Purchase #7 $95.47   13.189%   $108.0615   $108.06   $108.05   $108.10  
  7 purchase totals = $942.19       $1,022.7295   $1,022.73   $1,022.70   $1,022.80