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 $63.41   7.557%   $68.2019   $68.20   $68.20   $68.20  
  Purchase #2 $182.73   3.540%   $189.1986   $189.20   $189.20   $189.20  
  Purchase #3 $14.66   13.230%   $16.5995   $16.60   $16.60   $16.60  
  Purchase #4 $39.51   12.670%   $44.5159   $44.52   $44.50   $44.50  
  Purchase #5 $103.66   7.304%   $111.2313   $111.23   $111.25   $111.20  
  Purchase #6 $148.70   10.427%   $164.2049   $164.20   $164.20   $164.20  
  Purchase #7 $240.55   9.173%   $262.6157   $262.62   $262.60   $262.60  
  7 purchase totals = $793.22       $856.5678   $856.57   $856.55   $856.50