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	$75.38	3.550%	$78.056	$78.06	$78.05	$78.10
Purchase #2	$148.71	13.263%	$168.4334	$168.43	$168.45	$168.40
Purchase #3	$149.34	7.452%	$160.4688	$160.47	$160.45	$160.50
Purchase #4	$176.44	4.255%	$183.9475	$183.95	$183.95	$183.90
Purchase #5	$218.77	8.293%	$236.9126	$236.91	$236.90	$236.90
Purchase #6	$83.50	13.565%	$94.8268	$94.83	$94.85	$94.80
Purchase #7	$9.33	9.780%	$10.2425	$10.24	$10.25	$10.20
7 purchase totals =	$861.47		$932.8876	$932.89	$932.90	$932.80