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 $56.61   10.771%   $62.7075   $62.71   $62.70   $62.70  
  Purchase #2 $135.91   9.137%   $148.3281   $148.33   $148.35   $148.30  
  Purchase #3 $238.27   8.144%   $257.6747   $257.67   $257.65   $257.70  
  Purchase #4 $162.70   13.704%   $184.9964   $185.00   $185.00   $185.00  
  Purchase #5 $15.60   9.709%   $17.1146   $17.11   $17.10   $17.10  
  Purchase #6 $170.51   12.662%   $192.1   $192.10   $192.10   $192.10  
  Purchase #7 $103.49   12.744%   $116.6788   $116.68   $116.70   $116.70  
  7 purchase totals = $883.09       $979.6001   $979.60   $979.60   $979.60