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	$47.42	11.434%	$52.842	$52.84	$52.85	$52.80
Purchase #2	$209.43	6.440%	$222.9173	$222.92	$222.90	$222.90
Purchase #3	$85.84	5.182%	$90.2882	$90.29	$90.30	$90.30
Purchase #4	$81.72	5.687%	$86.3674	$86.37	$86.35	$86.40
Purchase #5	$152.36	9.192%	$166.3649	$166.36	$166.35	$166.40
Purchase #6	$169.63	5.109%	$178.2964	$178.30	$178.30	$178.30
Purchase #7	$82.27	10.672%	$91.0499	$91.05	$91.05	$91.00
7 purchase totals =	$828.67		$888.1261	$888.13	$888.10	$888.10