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	$202.51	3.143%	$208.8749	$208.87	$208.85	$208.90
Purchase #2	$42.43	9.397%	$46.4171	$46.42	$46.40	$46.40
Purchase #3	$98.85	13.486%	$112.1809	$112.18	$112.20	$112.20
Purchase #4	$137.91	10.115%	$151.8596	$151.86	$151.85	$151.90
Purchase #5	$115.96	11.188%	$128.9336	$128.93	$128.95	$128.90
Purchase #6	$102.26	12.184%	$114.7194	$114.72	$114.70	$114.70
Purchase #7	$82.46	10.663%	$91.2527	$91.25	$91.25	$91.30
7 purchase totals =	$782.38		$854.2382	$854.23	$854.20	$854.30