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	$99.80	6.425%	$106.2122	$106.21	$106.20	$106.20
Purchase #2	$203.35	9.483%	$222.6337	$222.63	$222.65	$222.60
Purchase #3	$66.25	7.552%	$71.2532	$71.25	$71.25	$71.30
Purchase #4	$191.62	6.333%	$203.7553	$203.76	$203.75	$203.80
Purchase #5	$78.78	11.442%	$87.794	$87.79	$87.80	$87.80
Purchase #6	$210.35	13.555%	$238.8629	$238.86	$238.85	$238.90
Purchase #7	$98.52	6.681%	$105.1021	$105.10	$105.10	$105.10
7 purchase totals =	$948.67		$1,035.6134	$1,035.60	$1,035.60	$1,035.70