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	$6.79	7.809%	$7.3202	$7.32	$7.30	$7.30
Purchase #2	$238.86	12.679%	$269.1451	$269.15	$269.15	$269.10
Purchase #3	$215.31	13.545%	$244.4737	$244.47	$244.45	$244.50
Purchase #4	$153.58	11.591%	$171.3815	$171.38	$171.40	$171.40
Purchase #5	$77.81	11.824%	$87.0103	$87.01	$87.00	$87.00
Purchase #6	$182.47	9.817%	$200.3831	$200.38	$200.40	$200.40
Purchase #7	$168.51	13.424%	$191.1308	$191.13	$191.15	$191.10
7 purchase totals =	$1,043.33		$1,170.8447	$1,170.84	$1,170.85	$1,170.80