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	$23.94	6.690%	$25.5416	$25.54	$25.55	$25.50
Purchase #2	$144.62	8.678%	$157.1701	$157.17	$157.15	$157.20
Purchase #3	$166.62	11.323%	$185.4864	$185.49	$185.50	$185.50
Purchase #4	$182.80	7.240%	$196.0347	$196.03	$196.05	$196.00
Purchase #5	$243.68	7.332%	$261.5466	$261.55	$261.55	$261.50
Purchase #6	$213.48	7.407%	$229.2925	$229.29	$229.30	$229.30
Purchase #7	$77.32	11.565%	$86.2621	$86.26	$86.25	$86.30
7 purchase totals =	$1,052.46		$1,141.3340	$1,141.33	$1,141.35	$1,141.30