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	$221.99	9.648%	$243.4076	$243.41	$243.40	$243.40
Purchase #2	$250.39	11.207%	$278.4512	$278.45	$278.45	$278.50
Purchase #3	$139.27	9.544%	$152.5619	$152.56	$152.55	$152.60
Purchase #4	$182.96	7.583%	$196.8339	$196.83	$196.85	$196.80
Purchase #5	$137.75	6.334%	$146.4751	$146.48	$146.50	$146.50
Purchase #6	$85.46	9.175%	$93.301	$93.30	$93.30	$93.30
Purchase #7	$30.84	6.215%	$32.7567	$32.76	$32.75	$32.80
7 purchase totals =	$1,048.66		$1,143.7874	$1,143.79	$1,143.80	$1,143.90