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	$209.63	12.830%	$236.5255	$236.53	$236.55	$236.50
Purchase #2	$92.72	13.667%	$105.392	$105.39	$105.40	$105.40
Purchase #3	$75.43	4.118%	$78.5362	$78.54	$78.55	$78.50
Purchase #4	$11.37	7.676%	$12.2428	$12.24	$12.25	$12.20
Purchase #5	$227.92	7.855%	$245.8231	$245.82	$245.80	$245.80
Purchase #6	$31.96	10.781%	$35.4056	$35.41	$35.40	$35.40
Purchase #7	$209.49	11.290%	$233.1414	$233.14	$233.15	$233.10
7 purchase totals =	$858.52		$947.0666	$947.07	$947.10	$946.90