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	$78.71	8.127%	$85.1068	$85.11	$85.10	$85.10
Purchase #2	$129.28	9.499%	$141.5603	$141.56	$141.55	$141.60
Purchase #3	$16.34	13.165%	$18.4912	$18.49	$18.50	$18.50
Purchase #4	$129.91	9.441%	$142.1748	$142.17	$142.15	$142.20
Purchase #5	$88.30	13.192%	$99.9485	$99.95	$99.95	$99.90
Purchase #6	$226.50	4.436%	$236.5475	$236.55	$236.55	$236.50
Purchase #7	$186.57	4.259%	$194.516	$194.52	$194.50	$194.50
7 purchase totals =	$855.61		$918.3451	$918.35	$918.30	$918.30