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	$169.56	11.696%	$189.3917	$189.39	$189.40	$189.40
Purchase #2	$30.86	9.417%	$33.7661	$33.77	$33.75	$33.80
Purchase #3	$137.99	7.633%	$148.5228	$148.52	$148.50	$148.50
Purchase #4	$173.31	6.700%	$184.9218	$184.92	$184.90	$184.90
Purchase #5	$78.95	3.118%	$81.4117	$81.41	$81.40	$81.40
Purchase #6	$90.32	10.279%	$99.604	$99.60	$99.60	$99.60
Purchase #7	$30.79	3.400%	$31.8369	$31.84	$31.85	$31.80
7 purchase totals =	$711.78		$769.4550	$769.45	$769.40	$769.40