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 $214.81   11.616%   $239.7623   $239.76   $239.75   $239.80  
  Purchase #2 $244.67   3.343%   $252.8493   $252.85   $252.85   $252.80  
  Purchase #3 $44.77   12.323%   $50.287   $50.29   $50.30   $50.30  
  Purchase #4 $56.38   12.531%   $63.445   $63.45   $63.45   $63.40  
  Purchase #5 $226.85   4.450%   $236.9448   $236.94   $236.95   $236.90  
  Purchase #6 $189.71   6.837%   $202.6805   $202.68   $202.70   $202.70  
  Purchase #7 $64.88   6.680%   $69.214   $69.21   $69.20   $69.20  
  7 purchase totals = $1,042.07       $1,115.1829   $1,115.18   $1,115.20   $1,115.10