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	$98.43	5.171%	$103.5198	$103.52	$103.50	$103.50
Purchase #2	$224.49	12.737%	$253.0833	$253.08	$253.10	$253.10
Purchase #3	$101.77	13.710%	$115.7227	$115.72	$115.70	$115.70
Purchase #4	$46.36	6.365%	$49.3108	$49.31	$49.30	$49.30
Purchase #5	$133.57	4.238%	$139.2307	$139.23	$139.25	$139.20
Purchase #6	$76.59	12.444%	$86.1209	$86.12	$86.10	$86.10
Purchase #7	$139.52	7.746%	$150.3272	$150.33	$150.35	$150.30
7 purchase totals =	$820.73		$897.3154	$897.31	$897.30	$897.20