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	$99.76	3.132%	$102.8845	$102.88	$102.90	$102.90
Purchase #2	$250.74	12.114%	$281.1146	$281.11	$281.10	$281.10
Purchase #3	$90.79	9.358%	$99.2861	$99.29	$99.30	$99.30
Purchase #4	$94.61	8.360%	$102.5194	$102.52	$102.50	$102.50
Purchase #5	$71.91	7.380%	$77.217	$77.22	$77.20	$77.20
Purchase #6	$148.52	9.319%	$162.3606	$162.36	$162.35	$162.40
Purchase #7	$214.59	10.482%	$237.0833	$237.08	$237.10	$237.10
7 purchase totals =	$970.92		$1,062.4655	$1,062.46	$1,062.45	$1,062.50