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	$82.58	4.427%	$86.2358	$86.24	$86.25	$86.20
Purchase #2	$36.43	8.740%	$39.614	$39.61	$39.60	$39.60
Purchase #3	$82.87	9.238%	$90.5255	$90.53	$90.55	$90.50
Purchase #4	$196.99	8.502%	$213.7381	$213.74	$213.75	$213.70
Purchase #5	$58.67	9.343%	$64.1515	$64.15	$64.15	$64.20
Purchase #6	$114.27	12.522%	$128.5789	$128.58	$128.60	$128.60
Purchase #7	$40.79	6.793%	$43.5609	$43.56	$43.55	$43.60
7 purchase totals =	$612.60		$666.4047	$666.41	$666.45	$666.40