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 $63.26   3.136%   $65.2438   $65.24   $65.25   $65.20  
  Purchase #2 $190.68   8.585%   $207.0499   $207.05   $207.05   $207.00  
  Purchase #3 $174.55   6.297%   $185.5414   $185.54   $185.55   $185.50  
  Purchase #4 $118.60   13.694%   $134.8411   $134.84   $134.85   $134.80  
  Purchase #5 $115.29   10.771%   $127.7079   $127.71   $127.70   $127.70  
  Purchase #6 $59.33   10.838%   $65.7602   $65.76   $65.75   $65.80  
  Purchase #7 $152.96   10.111%   $168.4258   $168.43   $168.45   $168.40  
  7 purchase totals = $874.67       $954.5701   $954.57   $954.60   $954.40