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	$91.28	8.492%	$99.0315	$99.03	$99.05	$99.00
Purchase #2	$127.89	7.371%	$137.3168	$137.32	$137.30	$137.30
Purchase #3	$115.85	12.432%	$130.2525	$130.25	$130.25	$130.30
Purchase #4	$81.31	6.266%	$86.4049	$86.40	$86.40	$86.40
Purchase #5	$209.77	11.686%	$234.2837	$234.28	$234.30	$234.30
Purchase #6	$82.30	10.192%	$90.688	$90.69	$90.70	$90.70
Purchase #7	$236.74	11.251%	$263.3756	$263.38	$263.40	$263.40
7 purchase totals =	$945.14		$1,041.3530	$1,041.35	$1,041.40	$1,041.40