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	$246.48	7.116%	$264.0195	$264.02	$264.00	$264.00
Purchase #2	$82.67	8.834%	$89.9731	$89.97	$89.95	$90.00
Purchase #3	$120.90	10.152%	$133.1738	$133.17	$133.15	$133.20
Purchase #4	$81.32	9.364%	$88.9348	$88.93	$88.95	$88.90
Purchase #5	$63.51	12.326%	$71.3382	$71.34	$71.35	$71.30
Purchase #6	$145.42	13.686%	$165.3222	$165.32	$165.30	$165.30
Purchase #7	$37.52	9.843%	$41.2131	$41.21	$41.20	$41.20
7 purchase totals =	$777.82		$853.9747	$853.96	$853.90	$853.90