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	$247.86	4.255%	$258.4064	$258.41	$258.40	$258.40
Purchase #2	$208.42	3.275%	$215.2458	$215.25	$215.25	$215.20
Purchase #3	$20.27	10.173%	$22.3321	$22.33	$22.35	$22.30
Purchase #4	$202.89	8.107%	$219.3383	$219.34	$219.35	$219.30
Purchase #5	$79.51	13.112%	$89.9354	$89.94	$89.95	$89.90
Purchase #6	$198.40	13.735%	$225.6502	$225.65	$225.65	$225.70
Purchase #7	$191.34	9.818%	$210.1258	$210.13	$210.15	$210.10
7 purchase totals =	$1,148.69		$1,241.0340	$1,241.05	$1,241.10	$1,240.90