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 $235.79   4.763%   $247.0207   $247.02   $247.00   $247.00  
  Purchase #2 $228.88   6.203%   $243.0774   $243.08   $243.10   $243.10  
  Purchase #3 $73.55   8.863%   $80.0687   $80.07   $80.05   $80.10  
  Purchase #4 $168.34   13.492%   $191.0524   $191.05   $191.05   $191.10  
  Purchase #5 $164.46   7.850%   $177.3701   $177.37   $177.35   $177.40  
  Purchase #6 $22.41   6.622%   $23.894   $23.89   $23.90   $23.90  
  Purchase #7 $199.67   7.243%   $214.1321   $214.13   $214.15   $214.10  
  7 purchase totals = $1,093.10       $1,176.6154   $1,176.61   $1,176.60   $1,176.70