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	$76.86	7.874%	$82.912	$82.91	$82.90	$82.90
Purchase #2	$73.60	3.510%	$76.1834	$76.18	$76.20	$76.20
Purchase #3	$48.96	7.529%	$52.6462	$52.65	$52.65	$52.60
Purchase #4	$190.48	3.638%	$197.4097	$197.41	$197.40	$197.40
Purchase #5	$78.66	10.468%	$86.8941	$86.89	$86.90	$86.90
Purchase #6	$83.28	7.253%	$89.3203	$89.32	$89.30	$89.30
Purchase #7	$198.65	11.670%	$221.8325	$221.83	$221.85	$221.80
7 purchase totals =	$750.49		$807.1982	$807.19	$807.20	$807.10