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	$42.59	6.744%	$45.4623	$45.46	$45.45	$45.50
Purchase #2	$150.50	3.645%	$155.9857	$155.99	$156.00	$156.00
Purchase #3	$106.97	9.699%	$117.345	$117.35	$117.35	$117.30
Purchase #4	$27.76	7.533%	$29.8512	$29.85	$29.85	$29.90
Purchase #5	$102.87	6.282%	$109.3323	$109.33	$109.35	$109.30
Purchase #6	$82.89	12.767%	$93.4726	$93.47	$93.45	$93.50
Purchase #7	$96.99	12.433%	$109.0488	$109.05	$109.05	$109.00
7 purchase totals =	$610.57		$660.4979	$660.50	$660.50	$660.50