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	$243.40	13.343%	$275.8769	$275.88	$275.90	$275.90
Purchase #2	$155.29	5.794%	$164.2875	$164.29	$164.30	$164.30
Purchase #3	$171.72	9.459%	$187.963	$187.96	$187.95	$188.00
Purchase #4	$159.58	7.597%	$171.7033	$171.70	$171.70	$171.70
Purchase #5	$95.88	6.594%	$102.2023	$102.20	$102.20	$102.20
Purchase #6	$229.33	10.437%	$253.2652	$253.27	$253.25	$253.30
Purchase #7	$69.96	3.469%	$72.3869	$72.39	$72.40	$72.40
7 purchase totals =	$1,125.16		$1,227.6851	$1,227.69	$1,227.70	$1,227.80