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	$75.78	12.767%	$85.4548	$85.45	$85.45	$85.50
Purchase #2	$61.55	9.383%	$67.3252	$67.33	$67.35	$67.30
Purchase #3	$242.74	8.860%	$264.2468	$264.25	$264.25	$264.20
Purchase #4	$181.52	9.575%	$198.9005	$198.90	$198.90	$198.90
Purchase #5	$105.40	13.746%	$119.8883	$119.89	$119.90	$119.90
Purchase #6	$173.53	12.557%	$195.3202	$195.32	$195.30	$195.30
Purchase #7	$164.28	9.117%	$179.2574	$179.26	$179.25	$179.30
7 purchase totals =	$1,004.80		$1,110.3932	$1,110.40	$1,110.40	$1,110.40