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	$122.29	7.842%	$131.88	$131.88	$131.90	$131.90
Purchase #2	$86.44	6.710%	$92.2401	$92.24	$92.25	$92.20
Purchase #3	$185.84	5.361%	$195.8029	$195.80	$195.80	$195.80
Purchase #4	$165.36	4.295%	$172.4622	$172.46	$172.45	$172.50
Purchase #5	$84.82	6.609%	$90.4258	$90.43	$90.45	$90.40
Purchase #6	$26.45	8.616%	$28.7289	$28.73	$28.75	$28.70
Purchase #7	$174.34	9.269%	$190.4996	$190.50	$190.50	$190.50
7 purchase totals =	$845.54		$902.0395	$902.04	$902.10	$902.00