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	$85.55	5.102%	$89.9148	$89.91	$89.90	$89.90
Purchase #2	$86.54	11.642%	$96.615	$96.62	$96.60	$96.60
Purchase #3	$242.41	9.198%	$264.7069	$264.71	$264.70	$264.70
Purchase #4	$142.27	7.570%	$153.0398	$153.04	$153.05	$153.00
Purchase #5	$217.62	10.390%	$240.2307	$240.23	$240.25	$240.20
Purchase #6	$246.76	10.454%	$272.5563	$272.56	$272.55	$272.60
Purchase #7	$63.32	6.342%	$67.3358	$67.34	$67.35	$67.30
7 purchase totals =	$1,084.47		$1,184.3993	$1,184.41	$1,184.40	$1,184.30