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 $246.54   3.128%   $254.2518   $254.25   $254.25   $254.30  
  Purchase #2 $26.43   5.715%   $27.9405   $27.94   $27.95   $27.90  
  Purchase #3 $33.60   3.162%   $34.6624   $34.66   $34.65   $34.70  
  Purchase #4 $187.53   11.668%   $209.411   $209.41   $209.40   $209.40  
  Purchase #5 $178.43   10.380%   $196.951   $196.95   $196.95   $197.00  
  Purchase #6 $66.43   4.319%   $69.2991   $69.30   $69.30   $69.30  
  Purchase #7 $194.98   7.303%   $209.2194   $209.22   $209.20   $209.20  
  7 purchase totals = $933.94       $1,001.7352   $1,001.73   $1,001.70   $1,001.80