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	$75.41	6.800%	$80.5379	$80.54	$80.55	$80.50
Purchase #2	$131.97	13.869%	$150.2729	$150.27	$150.25	$150.30
Purchase #3	$146.28	13.646%	$166.2414	$166.24	$166.25	$166.20
Purchase #4	$78.41	4.648%	$82.0545	$82.05	$82.05	$82.10
Purchase #5	$250.72	6.862%	$267.9244	$267.92	$267.90	$267.90
Purchase #6	$120.32	12.690%	$135.5886	$135.59	$135.60	$135.60
Purchase #7	$118.48	7.249%	$127.0686	$127.07	$127.05	$127.10
7 purchase totals =	$921.59		$1,009.6883	$1,009.68	$1,009.65	$1,009.70