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 $62.66   3.714%   $64.9872   $64.99   $65.00   $65.00  
  Purchase #2 $157.83   11.809%   $176.4681   $176.47   $176.45   $176.50  
  Purchase #3 $161.76   5.479%   $170.6228   $170.62   $170.60   $170.60  
  Purchase #4 $193.44   5.754%   $204.5705   $204.57   $204.55   $204.60  
  Purchase #5 $199.84   7.264%   $214.3564   $214.36   $214.35   $214.40  
  Purchase #6 $155.76   6.104%   $165.2676   $165.27   $165.25   $165.30  
  Purchase #7 $218.42   3.138%   $225.274   $225.27   $225.25   $225.30  
  7 purchase totals = $1,149.71       $1,221.5466   $1,221.55   $1,221.45   $1,221.70