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	$117.72	8.148%	$127.3118	$127.31	$127.30	$127.30
Purchase #2	$150.82	5.798%	$159.5645	$159.56	$159.55	$159.60
Purchase #3	$105.82	5.563%	$111.7068	$111.71	$111.70	$111.70
Purchase #4	$21.96	6.360%	$23.3567	$23.36	$23.35	$23.40
Purchase #5	$80.38	6.416%	$85.5372	$85.54	$85.55	$85.50
Purchase #6	$182.57	13.869%	$207.8906	$207.89	$207.90	$207.90
Purchase #7	$110.47	9.818%	$121.3159	$121.32	$121.30	$121.30
7 purchase totals =	$769.74		$836.6835	$836.69	$836.65	$836.70