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	$78.88	13.185%	$89.2803	$89.28	$89.30	$89.30
Purchase #2	$237.69	4.526%	$248.4478	$248.45	$248.45	$248.40
Purchase #3	$90.91	8.300%	$98.4555	$98.46	$98.45	$98.50
Purchase #4	$217.28	11.700%	$242.7018	$242.70	$242.70	$242.70
Purchase #5	$191.57	3.776%	$198.8037	$198.80	$198.80	$198.80
Purchase #6	$248.64	8.860%	$270.6695	$270.67	$270.65	$270.70
Purchase #7	$183.80	13.744%	$209.0615	$209.06	$209.05	$209.10
7 purchase totals =	$1,248.77		$1,357.4201	$1,357.42	$1,357.40	$1,357.50