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 $244.83   9.645%   $268.4439   $268.44   $268.45   $268.40  
  Purchase #2 $191.28   6.614%   $203.9313   $203.93   $203.95   $203.90  
  Purchase #3 $95.30   7.282%   $102.2397   $102.24   $102.25   $102.20  
  Purchase #4 $119.62   6.342%   $127.2063   $127.21   $127.20   $127.20  
  Purchase #5 $115.90   3.617%   $120.0921   $120.09   $120.10   $120.10  
  Purchase #6 $156.86   13.274%   $177.6816   $177.68   $177.70   $177.70  
  Purchase #7 $218.57   9.801%   $239.992   $239.99   $240.00   $240.00  
  7 purchase totals = $1,142.36       $1,239.5869   $1,239.58   $1,239.65   $1,239.50