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 $197.40   4.479%   $206.2415   $206.24   $206.25   $206.20  
  Purchase #2 $179.26   9.171%   $195.6999   $195.70   $195.70   $195.70  
  Purchase #3 $79.80   12.152%   $89.4973   $89.50   $89.50   $89.50  
  Purchase #4 $38.36   5.279%   $40.385   $40.39   $40.40   $40.40  
  Purchase #5 $195.48   10.174%   $215.3681   $215.37   $215.35   $215.40  
  Purchase #6 $71.80   4.436%   $74.985   $74.99   $75.00   $75.00  
  Purchase #7 $153.29   4.604%   $160.3475   $160.35   $160.35   $160.30  
  7 purchase totals = $915.39       $982.5243   $982.54   $982.55   $982.50