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 $136.93   3.161%   $141.2584   $141.26   $141.25   $141.30  
  Purchase #2 $72.38   4.250%   $75.4562   $75.46   $75.45   $75.50  
  Purchase #3 $204.80   7.218%   $219.5825   $219.58   $219.60   $219.60  
  Purchase #4 $245.26   5.633%   $259.0755   $259.08   $259.10   $259.10  
  Purchase #5 $208.59   3.511%   $215.9136   $215.91   $215.90   $215.90  
  Purchase #6 $225.32   6.300%   $239.5152   $239.52   $239.50   $239.50  
  Purchase #7 $55.99   5.327%   $58.9726   $58.97   $58.95   $59.00  
  7 purchase totals = $1,149.27       $1,209.7740   $1,209.78   $1,209.75   $1,209.90