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	$229.42	7.335%	$246.248	$246.25	$246.25	$246.20
Purchase #2	$139.32	9.285%	$152.2559	$152.26	$152.25	$152.30
Purchase #3	$158.62	7.108%	$169.8947	$169.89	$169.90	$169.90
Purchase #4	$83.85	6.392%	$89.2097	$89.21	$89.20	$89.20
Purchase #5	$89.35	4.217%	$93.1179	$93.12	$93.10	$93.10
Purchase #6	$165.33	9.499%	$181.0347	$181.03	$181.05	$181.00
Purchase #7	$87.61	12.432%	$98.5017	$98.50	$98.50	$98.50
7 purchase totals =	$953.50		$1,030.2626	$1,030.26	$1,030.25	$1,030.20