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	$125.69	13.261%	$142.3578	$142.36	$142.35	$142.40
Purchase #2	$186.67	12.406%	$209.8283	$209.83	$209.85	$209.80
Purchase #3	$222.67	9.313%	$243.4073	$243.41	$243.40	$243.40
Purchase #4	$123.80	5.481%	$130.5855	$130.59	$130.60	$130.60
Purchase #5	$169.79	10.220%	$187.1425	$187.14	$187.15	$187.10
Purchase #6	$6.33	6.213%	$6.7233	$6.72	$6.70	$6.70
Purchase #7	$94.83	6.154%	$100.6658	$100.67	$100.65	$100.70
7 purchase totals =	$929.78		$1,020.7105	$1,020.72	$1,020.70	$1,020.70