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	$39.94	12.854%	$45.0739	$45.07	$45.05	$45.10
Purchase #2	$189.66	3.812%	$196.8898	$196.89	$196.90	$196.90
Purchase #3	$218.26	10.443%	$241.0529	$241.05	$241.05	$241.10
Purchase #4	$38.29	13.686%	$43.5304	$43.53	$43.55	$43.50
Purchase #5	$55.55	12.740%	$62.6271	$62.63	$62.65	$62.60
Purchase #6	$162.29	8.265%	$175.7033	$175.70	$175.70	$175.70
Purchase #7	$150.58	10.204%	$165.9452	$165.95	$165.95	$165.90
7 purchase totals =	$854.57		$930.8226	$930.82	$930.85	$930.80