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	$99.89	10.590%	$110.4684	$110.47	$110.45	$110.50
Purchase #2	$128.54	9.114%	$140.2551	$140.26	$140.25	$140.30
Purchase #3	$211.25	5.240%	$222.3195	$222.32	$222.30	$222.30
Purchase #4	$81.61	8.299%	$88.3828	$88.38	$88.40	$88.40
Purchase #5	$78.43	8.812%	$85.3413	$85.34	$85.35	$85.30
Purchase #6	$123.63	8.672%	$134.3512	$134.35	$134.35	$134.40
Purchase #7	$92.32	6.873%	$98.6652	$98.67	$98.65	$98.70
7 purchase totals =	$815.67		$879.7835	$879.79	$879.75	$879.90