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	$129.93	9.223%	$141.9134	$141.91	$141.90	$141.90
Purchase #2	$100.43	9.393%	$109.8634	$109.86	$109.85	$109.90
Purchase #3	$171.46	7.800%	$184.8339	$184.83	$184.85	$184.80
Purchase #4	$37.90	11.625%	$42.3059	$42.31	$42.30	$42.30
Purchase #5	$102.76	3.741%	$106.6043	$106.60	$106.60	$106.60
Purchase #6	$75.77	11.536%	$84.5108	$84.51	$84.50	$84.50
Purchase #7	$166.35	9.170%	$181.6043	$181.60	$181.60	$181.60
7 purchase totals =	$784.60		$851.6360	$851.62	$851.60	$851.60