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	$133.42	10.113%	$146.9128	$146.91	$146.90	$146.90
Purchase #2	$225.36	7.607%	$242.5031	$242.50	$242.50	$242.50
Purchase #3	$31.41	6.603%	$33.484	$33.48	$33.50	$33.50
Purchase #4	$78.42	12.232%	$88.0123	$88.01	$88.00	$88.00
Purchase #5	$86.73	11.423%	$96.6372	$96.64	$96.65	$96.60
Purchase #6	$23.39	9.178%	$25.5367	$25.54	$25.55	$25.50
Purchase #7	$42.61	12.146%	$47.7854	$47.79	$47.80	$47.80
7 purchase totals =	$621.34		$680.8715	$680.87	$680.90	$680.80