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 $198.97   3.517%   $205.9678   $205.97   $205.95   $206.00  
  Purchase #2 $101.89   7.613%   $109.6469   $109.65   $109.65   $109.60  
  Purchase #3 $228.70   4.365%   $238.6828   $238.68   $238.70   $238.70  
  Purchase #4 $54.93   3.299%   $56.7421   $56.74   $56.75   $56.70  
  Purchase #5 $132.44   5.177%   $139.2964   $139.30   $139.30   $139.30  
  Purchase #6 $125.39   9.734%   $137.5955   $137.60   $137.60   $137.60  
  Purchase #7 $51.53   6.411%   $54.8336   $54.83   $54.85   $54.80  
  7 purchase totals = $893.85       $942.7651   $942.77   $942.80   $942.70