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	$187.78	11.428%	$209.2395	$209.24	$209.25	$209.20
Purchase #2	$212.38	5.438%	$223.9292	$223.93	$223.95	$223.90
Purchase #3	$205.83	13.486%	$233.5882	$233.59	$233.60	$233.60
Purchase #4	$35.33	7.249%	$37.8911	$37.89	$37.90	$37.90
Purchase #5	$185.40	9.517%	$203.0445	$203.04	$203.05	$203.00
Purchase #6	$239.92	4.772%	$251.369	$251.37	$251.35	$251.40
Purchase #7	$168.85	7.674%	$181.8075	$181.81	$181.80	$181.80
7 purchase totals =	$1,235.49		$1,340.8690	$1,340.87	$1,340.90	$1,340.80