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	$132.99	3.610%	$137.7909	$137.79	$137.80	$137.80
Purchase #2	$215.32	11.548%	$240.1852	$240.19	$240.20	$240.20
Purchase #3	$159.95	6.352%	$170.11	$170.11	$170.10	$170.10
Purchase #4	$54.49	4.407%	$56.8914	$56.89	$56.90	$56.90
Purchase #5	$78.76	13.689%	$89.5415	$89.54	$89.55	$89.50
Purchase #6	$160.30	6.700%	$171.0401	$171.04	$171.05	$171.00
Purchase #7	$213.70	13.848%	$243.2932	$243.29	$243.30	$243.30
7 purchase totals =	$1,015.51		$1,108.8523	$1,108.85	$1,108.90	$1,108.80