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	$107.88	6.219%	$114.5891	$114.59	$114.60	$114.60
Purchase #2	$165.29	8.483%	$179.3116	$179.31	$179.30	$179.30
Purchase #3	$168.26	7.569%	$180.9956	$181.00	$181.00	$181.00
Purchase #4	$74.94	4.762%	$78.5086	$78.51	$78.50	$78.50
Purchase #5	$22.80	12.317%	$25.6083	$25.61	$25.60	$25.60
Purchase #6	$59.85	12.752%	$67.4821	$67.48	$67.50	$67.50
Purchase #7	$181.59	4.206%	$189.2277	$189.23	$189.25	$189.20
7 purchase totals =	$780.61		$835.7230	$835.73	$835.75	$835.70