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	$209.79	9.317%	$229.3361	$229.34	$229.35	$229.30
Purchase #2	$78.68	13.851%	$89.578	$89.58	$89.60	$89.60
Purchase #3	$185.73	6.618%	$198.0216	$198.02	$198.00	$198.00
Purchase #4	$69.65	11.741%	$77.8276	$77.83	$77.85	$77.80
Purchase #5	$31.40	4.319%	$32.7562	$32.76	$32.75	$32.80
Purchase #6	$205.89	12.807%	$232.2583	$232.26	$232.25	$232.30
Purchase #7	$53.38	4.188%	$55.6156	$55.62	$55.60	$55.60
7 purchase totals =	$834.52		$915.3934	$915.41	$915.40	$915.40