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	$5.65	9.264%	$6.1734	$6.17	$6.15	$6.20
Purchase #2	$117.41	11.609%	$131.0401	$131.04	$131.05	$131.00
Purchase #3	$137.68	9.191%	$150.3342	$150.33	$150.35	$150.30
Purchase #4	$42.59	12.170%	$47.7732	$47.77	$47.75	$47.80
Purchase #5	$95.34	13.402%	$108.1175	$108.12	$108.10	$108.10
Purchase #6	$131.96	11.644%	$147.3254	$147.33	$147.35	$147.30
Purchase #7	$67.69	6.188%	$71.8787	$71.88	$71.90	$71.90
7 purchase totals =	$598.32		$662.6425	$662.64	$662.65	$662.60