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	$72.65	8.550%	$78.8616	$78.86	$78.85	$78.90
Purchase #2	$59.86	12.819%	$67.5335	$67.53	$67.55	$67.50
Purchase #3	$176.31	8.865%	$191.9399	$191.94	$191.95	$191.90
Purchase #4	$208.44	13.322%	$236.2084	$236.21	$236.20	$236.20
Purchase #5	$143.74	3.158%	$148.2793	$148.28	$148.30	$148.30
Purchase #6	$79.40	12.173%	$89.0654	$89.07	$89.05	$89.10
Purchase #7	$64.91	7.723%	$69.923	$69.92	$69.90	$69.90
7 purchase totals =	$805.31		$881.8111	$881.81	$881.80	$881.80