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	$147.96	8.851%	$161.0559	$161.06	$161.05	$161.10
Purchase #2	$78.64	13.777%	$89.4742	$89.47	$89.45	$89.50
Purchase #3	$21.48	7.612%	$23.1151	$23.12	$23.10	$23.10
Purchase #4	$205.70	9.292%	$224.8136	$224.81	$224.80	$224.80
Purchase #5	$6.92	13.399%	$7.8472	$7.85	$7.85	$7.80
Purchase #6	$152.42	10.539%	$168.4835	$168.48	$168.50	$168.50
Purchase #7	$139.79	11.681%	$156.1189	$156.12	$156.10	$156.10
7 purchase totals =	$752.91		$830.9084	$830.91	$830.85	$830.90