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	$20.77	3.152%	$21.4247	$21.42	$21.40	$21.40
Purchase #2	$116.77	11.223%	$129.8751	$129.88	$129.90	$129.90
Purchase #3	$209.59	12.232%	$235.227	$235.23	$235.25	$235.20
Purchase #4	$197.81	9.320%	$216.2459	$216.25	$216.25	$216.20
Purchase #5	$196.32	7.690%	$211.417	$211.42	$211.40	$211.40
Purchase #6	$218.82	4.792%	$229.3059	$229.31	$229.30	$229.30
Purchase #7	$51.48	6.767%	$54.9637	$54.96	$54.95	$55.00
7 purchase totals =	$1,011.56		$1,098.4593	$1,098.47	$1,098.45	$1,098.40