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	$175.70	8.711%	$191.0052	$191.01	$191.00	$191.00
Purchase #2	$51.79	6.754%	$55.2879	$55.29	$55.30	$55.30
Purchase #3	$218.85	11.569%	$244.1688	$244.17	$244.15	$244.20
Purchase #4	$39.91	4.638%	$41.761	$41.76	$41.75	$41.80
Purchase #5	$142.89	13.738%	$162.5202	$162.52	$162.50	$162.50
Purchase #6	$64.39	5.552%	$67.9649	$67.96	$67.95	$68.00
Purchase #7	$206.61	4.384%	$215.6678	$215.67	$215.65	$215.70
7 purchase totals =	$900.14		$978.3758	$978.38	$978.30	$978.50