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	$246.48	7.279%	$264.4213	$264.42	$264.40	$264.40
Purchase #2	$179.95	8.482%	$195.2134	$195.21	$195.20	$195.20
Purchase #3	$91.46	8.377%	$99.1216	$99.12	$99.10	$99.10
Purchase #4	$10.33	10.553%	$11.4201	$11.42	$11.40	$11.40
Purchase #5	$226.66	13.285%	$256.7718	$256.77	$256.75	$256.80
Purchase #6	$131.94	3.790%	$136.9405	$136.94	$136.95	$136.90
Purchase #7	$92.53	5.310%	$97.4433	$97.44	$97.45	$97.40
7 purchase totals =	$979.35		$1,061.3320	$1,061.32	$1,061.25	$1,061.20