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 $108.83   6.473%   $115.8746   $115.87   $115.85   $115.90  
  Purchase #2 $185.65   10.622%   $205.3697   $205.37   $205.35   $205.40  
  Purchase #3 $194.62   3.358%   $201.1553   $201.16   $201.15   $201.20  
  Purchase #4 $155.72   6.773%   $166.2669   $166.27   $166.25   $166.30  
  Purchase #5 $166.85   4.802%   $174.8621   $174.86   $174.85   $174.90  
  Purchase #6 $116.51   7.529%   $125.282   $125.28   $125.30   $125.30  
  Purchase #7 $15.50   6.670%   $16.5339   $16.53   $16.55   $16.50  
  7 purchase totals = $943.68       $1,005.3445   $1,005.34   $1,005.30   $1,005.50