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 $10.61   5.423%   $11.1854   $11.19   $11.20   $11.20  
  Purchase #2 $94.53   6.574%   $100.7444   $100.74   $100.75   $100.70  
  Purchase #3 $167.47   7.519%   $180.0621   $180.06   $180.05   $180.10  
  Purchase #4 $165.34   13.358%   $187.4261   $187.43   $187.45   $187.40  
  Purchase #5 $113.74   7.112%   $121.8292   $121.83   $121.85   $121.80  
  Purchase #6 $246.26   8.441%   $267.0468   $267.05   $267.05   $267.00  
  Purchase #7 $104.39   12.555%   $117.4962   $117.50   $117.50   $117.50  
  7 purchase totals = $902.34       $985.7902   $985.80   $985.85   $985.70