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 $84.77   13.678%   $96.3648   $96.36   $96.35   $96.40  
  Purchase #2 $156.56   9.631%   $171.6383   $171.64   $171.65   $171.60  
  Purchase #3 $81.29   6.134%   $86.2763   $86.28   $86.30   $86.30  
  Purchase #4 $122.85   8.245%   $132.979   $132.98   $133.00   $133.00  
  Purchase #5 $235.89   11.457%   $262.9159   $262.92   $262.90   $262.90  
  Purchase #6 $156.25   4.556%   $163.3688   $163.37   $163.35   $163.40  
  Purchase #7 $122.95   10.123%   $135.3962   $135.40   $135.40   $135.40  
  7 purchase totals = $960.56       $1,048.9393   $1,048.95   $1,048.95   $1,049.00