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 $196.73   6.207%   $208.941   $208.94   $208.95   $208.90  
  Purchase #2 $118.92   6.867%   $127.0862   $127.09   $127.10   $127.10  
  Purchase #3 $123.79   9.327%   $135.3359   $135.34   $135.35   $135.30  
  Purchase #4 $239.68   11.668%   $267.6459   $267.65   $267.65   $267.60  
  Purchase #5 $52.71   3.664%   $54.6413   $54.64   $54.65   $54.60  
  Purchase #6 $209.62   6.469%   $223.1803   $223.18   $223.20   $223.20  
  Purchase #7 $230.51   9.235%   $251.7976   $251.80   $251.80   $251.80  
  7 purchase totals = $1,171.96       $1,268.6282   $1,268.64   $1,268.70   $1,268.50