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	$30.41	10.356%	$33.5593	$33.56	$33.55	$33.60
Purchase #2	$240.39	13.672%	$273.2561	$273.26	$273.25	$273.30
Purchase #3	$236.85	3.809%	$245.8716	$245.87	$245.85	$245.90
Purchase #4	$159.77	3.470%	$165.314	$165.31	$165.30	$165.30
Purchase #5	$43.46	6.429%	$46.254	$46.25	$46.25	$46.30
Purchase #6	$115.53	13.765%	$131.4327	$131.43	$131.45	$131.40
Purchase #7	$16.36	6.257%	$17.3836	$17.38	$17.40	$17.40
7 purchase totals =	$842.77		$913.0713	$913.06	$913.05	$913.20