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	$236.48	3.143%	$243.9126	$243.91	$243.90	$243.90
Purchase #2	$79.95	11.400%	$89.0643	$89.06	$89.05	$89.10
Purchase #3	$47.87	13.649%	$54.4038	$54.40	$54.40	$54.40
Purchase #4	$16.86	8.230%	$18.2476	$18.25	$18.25	$18.20
Purchase #5	$28.82	8.862%	$31.374	$31.37	$31.35	$31.40
Purchase #6	$115.27	7.804%	$124.2657	$124.27	$124.25	$124.30
Purchase #7	$155.25	6.477%	$165.3055	$165.31	$165.30	$165.30
7 purchase totals =	$680.50		$726.5735	$726.57	$726.50	$726.60