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 $67.77   11.687%   $75.6903   $75.69   $75.70   $75.70  
  Purchase #2 $65.95   10.531%   $72.8952   $72.90   $72.90   $72.90  
  Purchase #3 $244.89   13.425%   $277.7665   $277.77   $277.75   $277.80  
  Purchase #4 $53.26   4.181%   $55.4868   $55.49   $55.50   $55.50  
  Purchase #5 $49.89   11.291%   $55.5231   $55.52   $55.50   $55.50  
  Purchase #6 $131.77   3.110%   $135.868   $135.87   $135.85   $135.90  
  Purchase #7 $249.33   6.374%   $265.2223   $265.22   $265.20   $265.20  
  7 purchase totals = $862.86       $938.4522   $938.46   $938.40   $938.50