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	$72.30	6.746%	$77.1774	$77.18	$77.20	$77.20
Purchase #2	$163.45	5.603%	$172.6081	$172.61	$172.60	$172.60
Purchase #3	$245.35	6.554%	$261.4302	$261.43	$261.45	$261.40
Purchase #4	$209.34	6.199%	$222.317	$222.32	$222.30	$222.30
Purchase #5	$19.94	3.350%	$20.608	$20.61	$20.60	$20.60
Purchase #6	$71.76	7.718%	$77.2984	$77.30	$77.30	$77.30
Purchase #7	$162.60	5.683%	$171.8406	$171.84	$171.85	$171.80
7 purchase totals =	$944.74		$1,003.2797	$1,003.29	$1,003.30	$1,003.20