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	$34.92	6.644%	$37.2401	$37.24	$37.25	$37.20
Purchase #2	$34.34	5.585%	$36.2579	$36.26	$36.25	$36.30
Purchase #3	$131.47	8.358%	$142.4583	$142.46	$142.45	$142.50
Purchase #4	$149.97	12.614%	$168.8872	$168.89	$168.90	$168.90
Purchase #5	$41.99	8.295%	$45.4731	$45.47	$45.45	$45.50
Purchase #6	$180.93	8.463%	$196.2421	$196.24	$196.25	$196.20
Purchase #7	$74.39	10.459%	$82.1705	$82.17	$82.15	$82.20
7 purchase totals =	$648.01		$708.7292	$708.73	$708.70	$708.80