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 $60.61   8.329%   $65.6582   $65.66   $65.65   $65.70  
  Purchase #2 $44.95   3.677%   $46.6028   $46.60   $46.60   $46.60  
  Purchase #3 $34.70   7.652%   $37.3552   $37.36   $37.35   $37.40  
  Purchase #4 $198.97   6.277%   $211.4593   $211.46   $211.45   $211.50  
  Purchase #5 $245.67   12.327%   $275.9537   $275.95   $275.95   $276.00  
  Purchase #6 $219.99   3.842%   $228.442   $228.44   $228.45   $228.40  
  Purchase #7 $87.89   5.750%   $92.9437   $92.94   $92.95   $92.90  
  7 purchase totals = $892.78       $958.4149   $958.41   $958.40   $958.50