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 $77.68   6.525%   $82.7486   $82.75   $82.75   $82.70  
  Purchase #2 $5.45   4.519%   $5.6963   $5.70   $5.70   $5.70  
  Purchase #3 $235.83   8.264%   $255.319   $255.32   $255.30   $255.30  
  Purchase #4 $101.27   3.557%   $104.8722   $104.87   $104.85   $104.90  
  Purchase #5 $160.68   6.722%   $171.4809   $171.48   $171.50   $171.50  
  Purchase #6 $209.69   10.582%   $231.8794   $231.88   $231.90   $231.90  
  Purchase #7 $102.48   6.554%   $109.1965   $109.20   $109.20   $109.20  
  7 purchase totals = $893.08       $961.1929   $961.20   $961.20   $961.20