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	$70.73	7.257%	$75.8629	$75.86	$75.85	$75.90
Purchase #2	$243.45	12.203%	$273.1582	$273.16	$273.15	$273.20
Purchase #3	$213.46	3.246%	$220.3889	$220.39	$220.40	$220.40
Purchase #4	$135.31	12.295%	$151.9464	$151.95	$151.95	$151.90
Purchase #5	$97.69	11.581%	$109.0035	$109.00	$109.00	$109.00
Purchase #6	$71.53	12.645%	$80.575	$80.58	$80.60	$80.60
Purchase #7	$60.69	11.840%	$67.8757	$67.88	$67.90	$67.90
7 purchase totals =	$892.86		$978.8106	$978.82	$978.85	$978.90