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 $193.87   4.114%   $201.8458   $201.85   $201.85   $201.80  
  Purchase #2 $72.26   12.547%   $81.3265   $81.33   $81.35   $81.30  
  Purchase #3 $71.55   4.475%   $74.7519   $74.75   $74.75   $74.80  
  Purchase #4 $234.29   12.152%   $262.7609   $262.76   $262.75   $262.80  
  Purchase #5 $107.99   10.860%   $119.7177   $119.72   $119.70   $119.70  
  Purchase #6 $108.64   9.763%   $119.2465   $119.25   $119.25   $119.20  
  Purchase #7 $202.81   9.637%   $222.3548   $222.35   $222.35   $222.40  
  7 purchase totals = $991.41       $1,082.0041   $1,082.01   $1,082.00   $1,082.00