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	$35.29	6.384%	$37.5429	$37.54	$37.55	$37.50
Purchase #2	$174.79	10.102%	$192.4473	$192.45	$192.45	$192.40
Purchase #3	$84.70	10.701%	$93.7637	$93.76	$93.75	$93.80
Purchase #4	$59.86	7.171%	$64.1526	$64.15	$64.15	$64.20
Purchase #5	$160.31	11.148%	$178.1814	$178.18	$178.20	$178.20
Purchase #6	$211.88	10.848%	$234.8647	$234.86	$234.85	$234.90
Purchase #7	$30.76	10.164%	$33.8864	$33.89	$33.90	$33.90
7 purchase totals =	$757.59		$834.8390	$834.83	$834.85	$834.90