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	$78.82	13.869%	$89.7515	$89.75	$89.75	$89.80
Purchase #2	$82.29	8.550%	$89.3258	$89.33	$89.35	$89.30
Purchase #3	$168.73	3.440%	$174.5343	$174.53	$174.55	$174.50
Purchase #4	$31.86	7.648%	$34.2967	$34.30	$34.30	$34.30
Purchase #5	$111.44	6.673%	$118.8764	$118.88	$118.90	$118.90
Purchase #6	$30.85	12.772%	$34.7902	$34.79	$34.80	$34.80
Purchase #7	$193.50	6.261%	$205.615	$205.62	$205.60	$205.60
7 purchase totals =	$697.49		$747.1899	$747.20	$747.25	$747.20