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	$136.81	8.123%	$147.9231	$147.92	$147.90	$147.90
Purchase #2	$196.56	13.145%	$222.3978	$222.40	$222.40	$222.40
Purchase #3	$142.51	11.609%	$159.054	$159.05	$159.05	$159.10
Purchase #4	$153.94	12.688%	$173.4719	$173.47	$173.45	$173.50
Purchase #5	$217.98	12.550%	$245.3365	$245.34	$245.35	$245.30
Purchase #6	$24.40	11.164%	$27.124	$27.12	$27.10	$27.10
Purchase #7	$245.80	7.427%	$264.0556	$264.06	$264.05	$264.10
7 purchase totals =	$1,118.00		$1,239.3629	$1,239.36	$1,239.30	$1,239.40