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	$81.52	12.242%	$91.4997	$91.50	$91.50	$91.50
Purchase #2	$161.82	8.477%	$175.5375	$175.54	$175.55	$175.50
Purchase #3	$46.81	3.260%	$48.336	$48.34	$48.35	$48.30
Purchase #4	$209.60	9.402%	$229.3066	$229.31	$229.30	$229.30
Purchase #5	$98.56	7.156%	$105.613	$105.61	$105.60	$105.60
Purchase #6	$73.85	9.136%	$80.5969	$80.60	$80.60	$80.60
Purchase #7	$126.47	3.168%	$130.4766	$130.48	$130.50	$130.50
7 purchase totals =	$798.63		$861.3663	$861.38	$861.40	$861.30