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	$70.90	10.696%	$78.4835	$78.48	$78.50	$78.50
Purchase #2	$32.48	3.596%	$33.648	$33.65	$33.65	$33.60
Purchase #3	$223.54	7.164%	$239.5544	$239.55	$239.55	$239.60
Purchase #4	$8.89	6.330%	$9.4527	$9.45	$9.45	$9.50
Purchase #5	$182.63	5.354%	$192.408	$192.41	$192.40	$192.40
Purchase #6	$247.56	9.805%	$271.8333	$271.83	$271.85	$271.80
Purchase #7	$165.59	6.164%	$175.797	$175.80	$175.80	$175.80
7 purchase totals =	$931.59		$1,001.1769	$1,001.17	$1,001.20	$1,001.20