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	$189.69	9.743%	$208.1715	$208.17	$208.15	$208.20
Purchase #2	$84.52	5.754%	$89.3833	$89.38	$89.40	$89.40
Purchase #3	$16.76	4.524%	$17.5182	$17.52	$17.50	$17.50
Purchase #4	$187.61	9.862%	$206.1121	$206.11	$206.10	$206.10
Purchase #5	$128.58	5.798%	$136.0351	$136.04	$136.05	$136.00
Purchase #6	$234.82	3.672%	$243.4426	$243.44	$243.45	$243.40
Purchase #7	$243.34	11.144%	$270.4578	$270.46	$270.45	$270.50
7 purchase totals =	$1,085.32		$1,171.1206	$1,171.12	$1,171.10	$1,171.10