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	$109.75	12.731%	$123.7223	$123.72	$123.70	$123.70
Purchase #2	$179.31	4.419%	$187.2337	$187.23	$187.25	$187.20
Purchase #3	$74.41	7.842%	$80.2452	$80.25	$80.25	$80.20
Purchase #4	$42.32	8.404%	$45.8766	$45.88	$45.90	$45.90
Purchase #5	$93.73	3.344%	$96.8643	$96.86	$96.85	$96.90
Purchase #6	$42.64	10.571%	$47.1475	$47.15	$47.15	$47.10
Purchase #7	$59.44	13.432%	$67.424	$67.42	$67.40	$67.40
7 purchase totals =	$601.60		$648.5136	$648.51	$648.50	$648.40