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	$73.29	5.363%	$77.2205	$77.22	$77.20	$77.20
Purchase #2	$73.89	12.634%	$83.2253	$83.23	$83.25	$83.20
Purchase #3	$82.56	13.860%	$94.0028	$94.00	$94.00	$94.00
Purchase #4	$130.27	13.279%	$147.5686	$147.57	$147.55	$147.60
Purchase #5	$81.25	10.592%	$89.856	$89.86	$89.85	$89.90
Purchase #6	$154.59	9.725%	$169.6239	$169.62	$169.60	$169.60
Purchase #7	$103.45	5.449%	$109.087	$109.09	$109.10	$109.10
7 purchase totals =	$699.30		$770.5841	$770.59	$770.55	$770.60