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	$69.96	12.768%	$78.8925	$78.89	$78.90	$78.90
Purchase #2	$238.56	4.606%	$249.5481	$249.55	$249.55	$249.50
Purchase #3	$110.77	5.171%	$116.4979	$116.50	$116.50	$116.50
Purchase #4	$82.86	10.258%	$91.3598	$91.36	$91.35	$91.40
Purchase #5	$168.36	12.179%	$188.8646	$188.86	$188.85	$188.90
Purchase #6	$171.84	11.532%	$191.6566	$191.66	$191.65	$191.70
Purchase #7	$53.87	9.201%	$58.8266	$58.83	$58.85	$58.80
7 purchase totals =	$896.22		$975.6461	$975.65	$975.65	$975.70