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	$170.33	10.613%	$188.4071	$188.41	$188.40	$188.40
Purchase #2	$41.50	8.842%	$45.1694	$45.17	$45.15	$45.20
Purchase #3	$58.75	13.545%	$66.7077	$66.71	$66.70	$66.70
Purchase #4	$94.29	7.445%	$101.3099	$101.31	$101.30	$101.30
Purchase #5	$59.68	8.744%	$64.8984	$64.90	$64.90	$64.90
Purchase #6	$35.54	8.338%	$38.5033	$38.50	$38.50	$38.50
Purchase #7	$247.46	13.316%	$280.4118	$280.41	$280.40	$280.40
7 purchase totals =	$707.55		$785.4076	$785.41	$785.35	$785.40