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 $62.82   12.518%   $70.6838   $70.68   $70.70   $70.70  
  Purchase #2 $152.93   3.813%   $158.7612   $158.76   $158.75   $158.80  
  Purchase #3 $211.44   6.743%   $225.6974   $225.70   $225.70   $225.70  
  Purchase #4 $149.72   7.119%   $160.3786   $160.38   $160.40   $160.40  
  Purchase #5 $50.95   8.396%   $55.2278   $55.23   $55.25   $55.20  
  Purchase #6 $66.25   3.353%   $68.4714   $68.47   $68.45   $68.50  
  Purchase #7 $15.26   7.495%   $16.4037   $16.40   $16.40   $16.40  
  7 purchase totals = $709.37       $755.6239   $755.62   $755.65   $755.70