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	$88.45	12.807%	$99.7778	$99.78	$99.80	$99.80
Purchase #2	$7.79	13.741%	$8.8604	$8.86	$8.85	$8.90
Purchase #3	$36.66	11.449%	$40.8572	$40.86	$40.85	$40.90
Purchase #4	$242.43	6.611%	$258.457	$258.46	$258.45	$258.50
Purchase #5	$34.98	11.630%	$39.0482	$39.05	$39.05	$39.00
Purchase #6	$90.84	6.624%	$96.8572	$96.86	$96.85	$96.90
Purchase #7	$104.51	5.689%	$110.4556	$110.46	$110.45	$110.50
7 purchase totals =	$605.66		$654.3134	$654.33	$654.30	$654.50