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 $168.61   5.262%   $177.4823   $177.48   $177.50   $177.50  
  Purchase #2 $250.65   9.145%   $273.5719   $273.57   $273.55   $273.60  
  Purchase #3 $204.76   3.165%   $211.2407   $211.24   $211.25   $211.20  
  Purchase #4 $151.33   10.687%   $167.5026   $167.50   $167.50   $167.50  
  Purchase #5 $183.64   4.373%   $191.6706   $191.67   $191.65   $191.70  
  Purchase #6 $24.71   4.292%   $25.7706   $25.77   $25.75   $25.80  
  Purchase #7 $82.34   3.279%   $85.0399   $85.04   $85.05   $85.00  
  7 purchase totals = $1,066.04       $1,132.2786   $1,132.27   $1,132.25   $1,132.30