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 $156.76   6.522%   $166.9839   $166.98   $167.00   $167.00  
  Purchase #2 $162.60   11.114%   $180.6714   $180.67   $180.65   $180.70  
  Purchase #3 $49.87   3.584%   $51.6573   $51.66   $51.65   $51.70  
  Purchase #4 $62.60   12.703%   $70.5521   $70.55   $70.55   $70.60  
  Purchase #5 $219.97   11.109%   $244.4065   $244.41   $244.40   $244.40  
  Purchase #6 $36.91   9.791%   $40.5239   $40.52   $40.50   $40.50  
  Purchase #7 $115.64   6.160%   $122.7634   $122.76   $122.75   $122.80  
  7 purchase totals = $804.35       $877.5585   $877.55   $877.50   $877.70