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	$72.48	10.779%	$80.2926	$80.29	$80.30	$80.30
Purchase #2	$222.64	13.871%	$253.5224	$253.52	$253.50	$253.50
Purchase #3	$180.97	9.283%	$197.7694	$197.77	$197.75	$197.80
Purchase #4	$120.94	8.431%	$131.1365	$131.14	$131.15	$131.10
Purchase #5	$204.80	13.423%	$232.2903	$232.29	$232.30	$232.30
Purchase #6	$189.89	13.625%	$215.7625	$215.76	$215.75	$215.80
Purchase #7	$100.71	4.639%	$105.3819	$105.38	$105.40	$105.40
7 purchase totals =	$1,092.43		$1,216.1556	$1,216.15	$1,216.15	$1,216.20