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 $164.63   13.212%   $186.3809   $186.38   $186.40   $186.40  
  Purchase #2 $196.72   3.341%   $203.2924   $203.29   $203.30   $203.30  
  Purchase #3 $161.91   7.701%   $174.3787   $174.38   $174.40   $174.40  
  Purchase #4 $92.56   9.123%   $101.0042   $101.00   $101.00   $101.00  
  Purchase #5 $57.47   13.584%   $65.2767   $65.28   $65.30   $65.30  
  Purchase #6 $240.89   8.320%   $260.932   $260.93   $260.95   $260.90  
  Purchase #7 $178.39   13.835%   $203.0703   $203.07   $203.05   $203.10  
  7 purchase totals = $1,092.57       $1,194.3352   $1,194.33   $1,194.40   $1,194.40