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	$21.67	7.630%	$23.3234	$23.32	$23.30	$23.30
Purchase #2	$168.31	12.426%	$189.2242	$189.22	$189.20	$189.20
Purchase #3	$216.25	5.644%	$228.4552	$228.46	$228.45	$228.50
Purchase #4	$240.37	10.107%	$264.6642	$264.66	$264.65	$264.70
Purchase #5	$81.72	9.241%	$89.2717	$89.27	$89.25	$89.30
Purchase #6	$33.94	5.832%	$35.9194	$35.92	$35.90	$35.90
Purchase #7	$20.50	6.150%	$21.7608	$21.76	$21.75	$21.80
7 purchase totals =	$782.76		$852.6189	$852.61	$852.50	$852.70