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	$32.75	10.644%	$36.2359	$36.24	$36.25	$36.20
Purchase #2	$161.42	13.435%	$183.1068	$183.11	$183.10	$183.10
Purchase #3	$173.54	8.300%	$187.9438	$187.94	$187.95	$187.90
Purchase #4	$78.78	13.347%	$89.2948	$89.29	$89.30	$89.30
Purchase #5	$245.91	5.520%	$259.4842	$259.48	$259.50	$259.50
Purchase #6	$71.63	13.601%	$81.3724	$81.37	$81.35	$81.40
Purchase #7	$35.25	8.617%	$38.2875	$38.29	$38.30	$38.30
7 purchase totals =	$799.28		$875.7254	$875.72	$875.75	$875.70