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	$148.76	7.279%	$159.5882	$159.59	$159.60	$159.60
Purchase #2	$19.71	6.435%	$20.9783	$20.98	$21.00	$21.00
Purchase #3	$248.70	7.709%	$267.8723	$267.87	$267.85	$267.90
Purchase #4	$89.87	4.719%	$94.111	$94.11	$94.10	$94.10
Purchase #5	$169.60	12.108%	$190.1352	$190.14	$190.15	$190.10
Purchase #6	$38.34	9.466%	$41.9693	$41.97	$41.95	$42.00
Purchase #7	$70.83	10.633%	$78.3614	$78.36	$78.35	$78.40
7 purchase totals =	$785.81		$853.0157	$853.02	$853.00	$853.10