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	$6.52	13.346%	$7.3902	$7.39	$7.40	$7.40
Purchase #2	$175.41	11.867%	$196.2259	$196.23	$196.25	$196.20
Purchase #3	$85.36	3.174%	$88.0693	$88.07	$88.05	$88.10
Purchase #4	$96.71	3.108%	$99.7157	$99.72	$99.70	$99.70
Purchase #5	$96.31	5.592%	$101.6957	$101.70	$101.70	$101.70
Purchase #6	$7.33	8.347%	$7.9418	$7.94	$7.95	$7.90
Purchase #7	$234.93	7.193%	$251.8285	$251.83	$251.85	$251.80
7 purchase totals =	$702.57		$752.8671	$752.88	$752.90	$752.80