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 $61.33   7.595%   $65.988   $65.99   $66.00   $66.00  
  Purchase #2 $124.32   5.812%   $131.5455   $131.55   $131.55   $131.50  
  Purchase #3 $44.74   11.319%   $49.8041   $49.80   $49.80   $49.80  
  Purchase #4 $231.51   3.180%   $238.872   $238.87   $238.85   $238.90  
  Purchase #5 $175.71   3.308%   $181.5225   $181.52   $181.50   $181.50  
  Purchase #6 $44.76   10.643%   $49.5238   $49.52   $49.50   $49.50  
  Purchase #7 $129.69   7.565%   $139.501   $139.50   $139.50   $139.50  
  7 purchase totals = $812.06       $856.7569   $856.75   $856.70   $856.70