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	$120.79	6.271%	$128.3647	$128.36	$128.35	$128.40
Purchase #2	$171.34	11.596%	$191.2086	$191.21	$191.20	$191.20
Purchase #3	$36.38	12.416%	$40.8969	$40.90	$40.90	$40.90
Purchase #4	$53.55	3.470%	$55.4082	$55.41	$55.40	$55.40
Purchase #5	$199.55	10.216%	$219.936	$219.94	$219.95	$219.90
Purchase #6	$165.75	4.651%	$173.459	$173.46	$173.45	$173.50
Purchase #7	$231.68	3.600%	$240.0205	$240.02	$240.00	$240.00
7 purchase totals =	$979.04		$1,049.2939	$1,049.30	$1,049.25	$1,049.30