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	$45.45	12.867%	$51.2981	$51.30	$51.30	$51.30
Purchase #2	$151.80	5.481%	$160.1202	$160.12	$160.10	$160.10
Purchase #3	$189.82	11.285%	$211.2412	$211.24	$211.25	$211.20
Purchase #4	$200.72	11.215%	$223.2307	$223.23	$223.25	$223.20
Purchase #5	$108.88	7.567%	$117.1189	$117.12	$117.10	$117.10
Purchase #6	$97.33	6.138%	$103.3041	$103.30	$103.30	$103.30
Purchase #7	$145.56	12.737%	$164.1	$164.10	$164.10	$164.10
7 purchase totals =	$939.56		$1,030.4132	$1,030.41	$1,030.40	$1,030.30