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 $182.53   3.551%   $189.0116   $189.01   $189.00   $189.00  
  Purchase #2 $58.76   3.136%   $60.6027   $60.60   $60.60   $60.60  
  Purchase #3 $170.72   3.657%   $176.9632   $176.96   $176.95   $177.00  
  Purchase #4 $71.67   6.564%   $76.3744   $76.37   $76.35   $76.40  
  Purchase #5 $131.83   8.420%   $142.9301   $142.93   $142.95   $142.90  
  Purchase #6 $231.46   5.208%   $243.5144   $243.51   $243.50   $243.50  
  Purchase #7 $231.45   5.159%   $243.3905   $243.39   $243.40   $243.40  
  7 purchase totals = $1,078.42       $1,132.7869   $1,132.77   $1,132.75   $1,132.80