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	$52.85	4.350%	$55.149	$55.15	$55.15	$55.10
Purchase #2	$71.45	6.111%	$75.8163	$75.82	$75.80	$75.80
Purchase #3	$159.98	13.251%	$181.1789	$181.18	$181.20	$181.20
Purchase #4	$81.72	4.484%	$85.3843	$85.38	$85.40	$85.40
Purchase #5	$37.36	13.327%	$42.339	$42.34	$42.35	$42.30
Purchase #6	$209.68	4.850%	$219.8495	$219.85	$219.85	$219.80
Purchase #7	$202.34	8.303%	$219.1403	$219.14	$219.15	$219.10
7 purchase totals =	$815.38		$878.8573	$878.86	$878.90	$878.70