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 $163.92   12.417%   $184.2739   $184.27   $184.25   $184.30  
  Purchase #2 $68.93   10.323%   $76.0456   $76.05   $76.05   $76.00  
  Purchase #3 $125.89   8.167%   $136.1714   $136.17   $136.15   $136.20  
  Purchase #4 $212.69   9.594%   $233.0955   $233.10   $233.10   $233.10  
  Purchase #5 $226.25   13.103%   $255.8955   $255.90   $255.90   $255.90  
  Purchase #6 $128.67   10.593%   $142.3   $142.30   $142.30   $142.30  
  Purchase #7 $235.54   4.695%   $246.5986   $246.60   $246.60   $246.60  
  7 purchase totals = $1,161.89       $1,274.3805   $1,274.39   $1,274.35   $1,274.40