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	$88.41	12.578%	$99.5302	$99.53	$99.55	$99.50
Purchase #2	$211.96	10.214%	$233.6096	$233.61	$233.60	$233.60
Purchase #3	$181.33	11.450%	$202.0923	$202.09	$202.10	$202.10
Purchase #4	$62.81	4.112%	$65.3927	$65.39	$65.40	$65.40
Purchase #5	$179.75	4.568%	$187.961	$187.96	$187.95	$188.00
Purchase #6	$154.25	9.131%	$168.3346	$168.33	$168.35	$168.30
Purchase #7	$232.98	13.589%	$264.6397	$264.64	$264.65	$264.60
7 purchase totals =	$1,111.49		$1,221.5601	$1,221.55	$1,221.60	$1,221.50