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	$167.55	10.717%	$185.5063	$185.51	$185.50	$185.50
Purchase #2	$79.86	12.137%	$89.5526	$89.55	$89.55	$89.60
Purchase #3	$121.84	7.815%	$131.3618	$131.36	$131.35	$131.40
Purchase #4	$25.73	9.514%	$28.178	$28.18	$28.20	$28.20
Purchase #5	$189.98	6.740%	$202.7847	$202.78	$202.80	$202.80
Purchase #6	$247.79	10.356%	$273.4511	$273.45	$273.45	$273.50
Purchase #7	$76.65	7.149%	$82.1297	$82.13	$82.15	$82.10
7 purchase totals =	$909.40		$992.9642	$992.96	$993.00	$993.10