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	$102.31	4.403%	$106.8147	$106.81	$106.80	$106.80
Purchase #2	$40.56	11.774%	$45.3355	$45.34	$45.35	$45.30
Purchase #3	$225.86	12.407%	$253.8825	$253.88	$253.90	$253.90
Purchase #4	$90.82	12.145%	$101.8501	$101.85	$101.85	$101.90
Purchase #5	$96.86	3.361%	$100.1155	$100.12	$100.10	$100.10
Purchase #6	$98.74	10.642%	$109.2479	$109.25	$109.25	$109.20
Purchase #7	$250.93	3.302%	$259.2157	$259.22	$259.20	$259.20
7 purchase totals =	$906.08		$976.4619	$976.47	$976.45	$976.40