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	$229.74	4.439%	$239.9382	$239.94	$239.95	$239.90
Purchase #2	$225.29	8.227%	$243.8246	$243.82	$243.80	$243.80
Purchase #3	$65.54	8.805%	$71.3108	$71.31	$71.30	$71.30
Purchase #4	$45.31	6.346%	$48.1854	$48.19	$48.20	$48.20
Purchase #5	$134.82	9.669%	$147.8557	$147.86	$147.85	$147.90
Purchase #6	$174.93	8.675%	$190.1052	$190.11	$190.10	$190.10
Purchase #7	$80.53	10.780%	$89.2111	$89.21	$89.20	$89.20
7 purchase totals =	$956.16		$1,030.4310	$1,030.44	$1,030.40	$1,030.40