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	$228.26	12.117%	$255.9183	$255.92	$255.90	$255.90
Purchase #2	$203.55	7.498%	$218.8122	$218.81	$218.80	$218.80
Purchase #3	$101.31	11.278%	$112.7357	$112.74	$112.75	$112.70
Purchase #4	$145.97	11.568%	$162.8558	$162.86	$162.85	$162.90
Purchase #5	$83.26	9.506%	$91.1747	$91.17	$91.15	$91.20
Purchase #6	$83.38	6.258%	$88.5979	$88.60	$88.60	$88.60
Purchase #7	$107.71	4.511%	$112.5688	$112.57	$112.55	$112.60
7 purchase totals =	$953.44		$1,042.6634	$1,042.67	$1,042.60	$1,042.70