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	$75.85	8.334%	$82.1713	$82.17	$82.15	$82.20
Purchase #2	$11.93	13.740%	$13.5692	$13.57	$13.55	$13.60
Purchase #3	$79.42	12.758%	$89.5524	$89.55	$89.55	$89.60
Purchase #4	$213.68	7.104%	$228.8598	$228.86	$228.85	$228.90
Purchase #5	$67.33	9.615%	$73.8038	$73.80	$73.80	$73.80
Purchase #6	$89.53	7.319%	$96.0827	$96.08	$96.10	$96.10
Purchase #7	$71.73	10.732%	$79.4281	$79.43	$79.45	$79.40
7 purchase totals =	$609.47		$663.4673	$663.46	$663.45	$663.60