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	$6.49	7.142%	$6.9535	$6.95	$6.95	$7.00
Purchase #2	$238.35	4.602%	$249.3189	$249.32	$249.30	$249.30
Purchase #3	$98.94	5.807%	$104.6854	$104.69	$104.70	$104.70
Purchase #4	$41.74	8.467%	$45.2741	$45.27	$45.25	$45.30
Purchase #5	$111.91	3.801%	$116.1637	$116.16	$116.15	$116.20
Purchase #6	$84.29	6.634%	$89.8818	$89.88	$89.90	$89.90
Purchase #7	$52.61	5.543%	$55.5262	$55.53	$55.55	$55.50
7 purchase totals =	$634.33		$667.8036	$667.80	$667.80	$667.90