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	$120.43	9.198%	$131.5072	$131.51	$131.50	$131.50
Purchase #2	$150.46	13.207%	$170.3313	$170.33	$170.35	$170.30
Purchase #3	$39.88	13.409%	$45.2275	$45.23	$45.25	$45.20
Purchase #4	$210.68	6.799%	$225.0041	$225.00	$225.00	$225.00
Purchase #5	$39.29	7.612%	$42.2808	$42.28	$42.30	$42.30
Purchase #6	$11.88	12.520%	$13.3674	$13.37	$13.35	$13.40
Purchase #7	$78.91	8.383%	$85.525	$85.53	$85.55	$85.50
7 purchase totals =	$651.53		$713.2433	$713.25	$713.30	$713.20