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	$25.89	11.387%	$28.8381	$28.84	$28.85	$28.80
Purchase #2	$166.83	11.271%	$185.6334	$185.63	$185.65	$185.60
Purchase #3	$143.56	11.682%	$160.3307	$160.33	$160.35	$160.30
Purchase #4	$189.80	7.371%	$203.7902	$203.79	$203.80	$203.80
Purchase #5	$233.35	9.356%	$255.1822	$255.18	$255.20	$255.20
Purchase #6	$115.83	8.189%	$125.3153	$125.32	$125.30	$125.30
Purchase #7	$98.34	3.653%	$101.9324	$101.93	$101.95	$101.90
7 purchase totals =	$973.60		$1,061.0223	$1,061.02	$1,061.10	$1,060.90