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	$250.86	8.251%	$271.5585	$271.56	$271.55	$271.60
Purchase #2	$171.76	11.455%	$191.4351	$191.44	$191.45	$191.40
Purchase #3	$26.80	11.262%	$29.8182	$29.82	$29.80	$29.80
Purchase #4	$99.90	11.655%	$111.5433	$111.54	$111.55	$111.50
Purchase #5	$101.60	10.377%	$112.143	$112.14	$112.15	$112.10
Purchase #6	$33.78	6.266%	$35.8967	$35.90	$35.90	$35.90
Purchase #7	$168.85	6.581%	$179.962	$179.96	$179.95	$180.00
7 purchase totals =	$853.55		$932.3568	$932.36	$932.35	$932.30