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	$128.75	13.423%	$146.0321	$146.03	$146.05	$146.00
Purchase #2	$206.29	13.114%	$233.3429	$233.34	$233.35	$233.30
Purchase #3	$119.82	9.157%	$130.7919	$130.79	$130.80	$130.80
Purchase #4	$101.84	11.865%	$113.9233	$113.92	$113.90	$113.90
Purchase #5	$62.73	13.244%	$71.038	$71.04	$71.05	$71.00
Purchase #6	$123.61	6.614%	$131.7856	$131.79	$131.80	$131.80
Purchase #7	$71.32	13.809%	$81.1686	$81.17	$81.15	$81.20
7 purchase totals =	$814.36		$908.0824	$908.08	$908.10	$908.00