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 $245.88   11.710%   $274.6725   $274.67   $274.65   $274.70  
  Purchase #2 $164.64   9.113%   $179.6436   $179.64   $179.65   $179.60  
  Purchase #3 $131.55   11.808%   $147.0834   $147.08   $147.10   $147.10  
  Purchase #4 $70.50   4.625%   $73.7606   $73.76   $73.75   $73.80  
  Purchase #5 $153.52   5.473%   $161.9221   $161.92   $161.90   $161.90  
  Purchase #6 $23.31   3.193%   $24.0543   $24.05   $24.05   $24.10  
  Purchase #7 $198.63   13.451%   $225.3477   $225.35   $225.35   $225.30  
  7 purchase totals = $988.03       $1,086.4842   $1,086.47   $1,086.45   $1,086.50