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 $180.94   12.384%   $203.3476   $203.35   $203.35   $203.30  
  Purchase #2 $221.63   6.241%   $235.4619   $235.46   $235.45   $235.50  
  Purchase #3 $100.61   10.813%   $111.489   $111.49   $111.50   $111.50  
  Purchase #4 $43.91   13.477%   $49.8278   $49.83   $49.85   $49.80  
  Purchase #5 $126.39   13.440%   $143.3768   $143.38   $143.40   $143.40  
  Purchase #6 $237.76   3.627%   $246.3836   $246.38   $246.40   $246.40  
  Purchase #7 $162.49   13.652%   $184.6731   $184.67   $184.65   $184.70  
  7 purchase totals = $1,073.73       $1,174.5598   $1,174.56   $1,174.60   $1,174.60