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 $143.57   10.680%   $158.9033   $158.90   $158.90   $158.90  
  Purchase #2 $179.28   8.127%   $193.8501   $193.85   $193.85   $193.90  
  Purchase #3 $77.76   10.210%   $85.6993   $85.70   $85.70   $85.70  
  Purchase #4 $232.79   5.174%   $244.8346   $244.83   $244.85   $244.80  
  Purchase #5 $203.31   10.413%   $224.4807   $224.48   $224.50   $224.50  
  Purchase #6 $58.30   10.122%   $64.2011   $64.20   $64.20   $64.20  
  Purchase #7 $84.73   11.711%   $94.6527   $94.65   $94.65   $94.70  
  7 purchase totals = $979.74       $1,066.6218   $1,066.61   $1,066.65   $1,066.70