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	$66.61	8.645%	$72.3684	$72.37	$72.35	$72.40
Purchase #2	$174.59	12.805%	$196.9462	$196.95	$196.95	$196.90
Purchase #3	$127.29	8.229%	$137.7647	$137.76	$137.75	$137.80
Purchase #4	$245.39	13.422%	$278.3262	$278.33	$278.35	$278.30
Purchase #5	$110.90	5.114%	$116.5714	$116.57	$116.55	$116.60
Purchase #6	$195.82	6.747%	$209.032	$209.03	$209.05	$209.00
Purchase #7	$9.59	7.505%	$10.3097	$10.31	$10.30	$10.30
7 purchase totals =	$930.19		$1,021.3186	$1,021.32	$1,021.30	$1,021.30