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 $176.72   11.557%   $197.1435   $197.14   $197.15   $197.10  
  Purchase #2 $132.42   7.597%   $142.4799   $142.48   $142.50   $142.50  
  Purchase #3 $87.48   4.115%   $91.0798   $91.08   $91.10   $91.10  
  Purchase #4 $221.62   4.485%   $231.5597   $231.56   $231.55   $231.60  
  Purchase #5 $66.43   4.141%   $69.1809   $69.18   $69.20   $69.20  
  Purchase #6 $157.34   11.594%   $175.582   $175.58   $175.60   $175.60  
  Purchase #7 $18.34   5.737%   $19.3922   $19.39   $19.40   $19.40  
  7 purchase totals = $860.35       $926.4180   $926.41   $926.50   $926.50