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	$220.96	11.293%	$245.913	$245.91	$245.90	$245.90
Purchase #2	$249.54	11.619%	$278.5341	$278.53	$278.55	$278.50
Purchase #3	$42.56	9.476%	$46.593	$46.59	$46.60	$46.60
Purchase #4	$60.44	11.843%	$67.5979	$67.60	$67.60	$67.60
Purchase #5	$77.64	5.266%	$81.7285	$81.73	$81.75	$81.70
Purchase #6	$25.90	11.702%	$28.9308	$28.93	$28.95	$28.90
Purchase #7	$248.44	8.230%	$268.8866	$268.89	$268.90	$268.90
7 purchase totals =	$925.48		$1,018.1839	$1,018.18	$1,018.25	$1,018.10