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	$179.66	5.293%	$189.1694	$189.17	$189.15	$189.20
Purchase #2	$18.69	8.711%	$20.3181	$20.32	$20.30	$20.30
Purchase #3	$26.25	9.788%	$28.8194	$28.82	$28.80	$28.80
Purchase #4	$88.47	8.416%	$95.9156	$95.92	$95.90	$95.90
Purchase #5	$89.73	4.632%	$93.8863	$93.89	$93.90	$93.90
Purchase #6	$205.82	8.717%	$223.7613	$223.76	$223.75	$223.80
Purchase #7	$156.86	5.631%	$165.6928	$165.69	$165.70	$165.70
7 purchase totals =	$765.48		$817.5629	$817.57	$817.50	$817.60