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 $87.55   12.230%   $98.2574   $98.26   $98.25   $98.30  
  Purchase #2 $98.37   8.685%   $106.9134   $106.91   $106.90   $106.90  
  Purchase #3 $234.87   5.565%   $247.9405   $247.94   $247.95   $247.90  
  Purchase #4 $169.41   9.654%   $185.7648   $185.76   $185.75   $185.80  
  Purchase #5 $195.98   4.442%   $204.6854   $204.69   $204.70   $204.70  
  Purchase #6 $176.26   6.370%   $187.4878   $187.49   $187.50   $187.50  
  Purchase #7 $185.44   8.688%   $201.551   $201.55   $201.55   $201.60  
  7 purchase totals = $1,147.88       $1,232.6003   $1,232.60   $1,232.60   $1,232.70