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 $66.96   5.313%   $70.5176   $70.52   $70.50   $70.50  
  Purchase #2 $137.89   11.763%   $154.11   $154.11   $154.10   $154.10  
  Purchase #3 $149.95   10.673%   $165.9542   $165.95   $165.95   $166.00  
  Purchase #4 $198.99   5.851%   $210.6329   $210.63   $210.65   $210.60  
  Purchase #5 $72.54   7.610%   $78.0603   $78.06   $78.05   $78.10  
  Purchase #6 $228.54   9.691%   $250.6878   $250.69   $250.70   $250.70  
  Purchase #7 $32.67   9.222%   $35.6828   $35.68   $35.70   $35.70  
  7 purchase totals = $887.54       $965.6456   $965.64   $965.65   $965.70