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	$128.84	8.463%	$139.7437	$139.74	$139.75	$139.70
Purchase #2	$119.63	11.507%	$133.3958	$133.40	$133.40	$133.40
Purchase #3	$67.94	6.368%	$72.2664	$72.27	$72.25	$72.30
Purchase #4	$42.58	12.467%	$47.8884	$47.89	$47.90	$47.90
Purchase #5	$154.48	13.764%	$175.7426	$175.74	$175.75	$175.70
Purchase #6	$48.88	8.756%	$53.1599	$53.16	$53.15	$53.20
Purchase #7	$115.97	9.725%	$127.2481	$127.25	$127.25	$127.20
7 purchase totals =	$678.32		$749.4449	$749.45	$749.45	$749.40