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	$36.96	12.346%	$41.5231	$41.52	$41.50	$41.50
Purchase #2	$94.25	8.709%	$102.4582	$102.46	$102.45	$102.50
Purchase #3	$68.81	7.722%	$74.1235	$74.12	$74.10	$74.10
Purchase #4	$89.45	3.270%	$92.375	$92.38	$92.40	$92.40
Purchase #5	$26.53	5.102%	$27.8836	$27.88	$27.90	$27.90
Purchase #6	$156.40	5.824%	$165.5087	$165.51	$165.50	$165.50
Purchase #7	$128.72	7.552%	$138.4409	$138.44	$138.45	$138.40
7 purchase totals =	$601.12		$642.3130	$642.31	$642.30	$642.30