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 $94.57   7.566%   $101.7252   $101.73   $101.75   $101.70  
  Purchase #2 $244.91   12.296%   $275.0241   $275.02   $275.00   $275.00  
  Purchase #3 $178.25   6.548%   $189.9218   $189.92   $189.90   $189.90  
  Purchase #4 $24.95   4.283%   $26.0186   $26.02   $26.00   $26.00  
  Purchase #5 $178.30   3.820%   $185.1111   $185.11   $185.10   $185.10  
  Purchase #6 $183.76   13.668%   $208.8763   $208.88   $208.90   $208.90  
  Purchase #7 $229.31   5.249%   $241.3465   $241.35   $241.35   $241.30  
  7 purchase totals = $1,134.05       $1,228.0236   $1,228.03   $1,228.00   $1,227.90