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	$139.39	6.230%	$148.074	$148.07	$148.05	$148.10
Purchase #2	$150.72	9.619%	$165.2178	$165.22	$165.20	$165.20
Purchase #3	$66.77	8.523%	$72.4608	$72.46	$72.45	$72.50
Purchase #4	$81.49	12.541%	$91.7097	$91.71	$91.70	$91.70
Purchase #5	$17.83	6.207%	$18.9367	$18.94	$18.95	$18.90
Purchase #6	$47.56	8.235%	$51.4766	$51.48	$51.50	$51.50
Purchase #7	$227.91	6.860%	$243.5446	$243.54	$243.55	$243.50
7 purchase totals =	$731.67		$791.4202	$791.42	$791.40	$791.40