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 $103.78   8.749%   $112.8597   $112.86   $112.85   $112.90  
  Purchase #2 $99.34   11.571%   $110.8346   $110.83   $110.85   $110.80  
  Purchase #3 $200.81   12.564%   $226.0398   $226.04   $226.05   $226.00  
  Purchase #4 $169.94   3.401%   $175.7197   $175.72   $175.70   $175.70  
  Purchase #5 $248.68   5.492%   $262.3375   $262.34   $262.35   $262.30  
  Purchase #6 $101.63   8.386%   $110.1527   $110.15   $110.15   $110.20  
  Purchase #7 $61.91   5.567%   $65.3565   $65.36   $65.35   $65.40  
  7 purchase totals = $986.09       $1,063.3005   $1,063.30   $1,063.30   $1,063.30