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	$172.80	7.194%	$185.2312	$185.23	$185.25	$185.20
Purchase #2	$189.64	13.433%	$215.1143	$215.11	$215.10	$215.10
Purchase #3	$79.43	4.799%	$83.2418	$83.24	$83.25	$83.20
Purchase #4	$131.41	6.320%	$139.7151	$139.72	$139.70	$139.70
Purchase #5	$186.66	5.174%	$196.3178	$196.32	$196.30	$196.30
Purchase #6	$206.75	7.498%	$222.2521	$222.25	$222.25	$222.30
Purchase #7	$8.58	6.134%	$9.1063	$9.11	$9.10	$9.10
7 purchase totals =	$975.27		$1,050.9786	$1,050.98	$1,050.95	$1,050.90