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	$96.91	3.534%	$100.3348	$100.33	$100.35	$100.30
Purchase #2	$147.88	3.180%	$152.5826	$152.58	$152.60	$152.60
Purchase #3	$168.53	3.734%	$174.8229	$174.82	$174.80	$174.80
Purchase #4	$65.26	9.437%	$71.4186	$71.42	$71.40	$71.40
Purchase #5	$174.53	4.122%	$181.7241	$181.72	$181.70	$181.70
Purchase #6	$47.41	11.613%	$52.9157	$52.92	$52.90	$52.90
Purchase #7	$99.84	11.829%	$111.6501	$111.65	$111.65	$111.70
7 purchase totals =	$800.36		$845.4488	$845.44	$845.40	$845.40