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 $76.83   11.580%   $85.7269   $85.73   $85.75   $85.70  
  Purchase #2 $167.93   10.410%   $185.4115   $185.41   $185.40   $185.40  
  Purchase #3 $204.68   5.260%   $215.4462   $215.45   $215.45   $215.40  
  Purchase #4 $79.35   10.597%   $87.7587   $87.76   $87.75   $87.80  
  Purchase #5 $53.75   5.291%   $56.5939   $56.59   $56.60   $56.60  
  Purchase #6 $224.64   12.258%   $252.1764   $252.18   $252.20   $252.20  
  Purchase #7 $68.96   5.191%   $72.5397   $72.54   $72.55   $72.50  
  7 purchase totals = $876.14       $955.6533   $955.66   $955.70   $955.60