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	$64.59	12.587%	$72.7199	$72.72	$72.70	$72.70
Purchase #2	$63.88	5.402%	$67.3308	$67.33	$67.35	$67.30
Purchase #3	$156.48	12.661%	$176.2919	$176.29	$176.30	$176.30
Purchase #4	$91.42	7.242%	$98.0406	$98.04	$98.05	$98.00
Purchase #5	$241.50	11.736%	$269.8424	$269.84	$269.85	$269.80
Purchase #6	$75.42	4.367%	$78.7136	$78.71	$78.70	$78.70
Purchase #7	$147.75	9.203%	$161.3474	$161.35	$161.35	$161.30
7 purchase totals =	$841.04		$924.2866	$924.28	$924.30	$924.10