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	$135.95	3.318%	$140.4608	$140.46	$140.45	$140.50
Purchase #2	$249.85	9.456%	$273.4758	$273.48	$273.50	$273.50
Purchase #3	$231.91	5.111%	$243.7629	$243.76	$243.75	$243.80
Purchase #4	$183.95	11.617%	$205.3195	$205.32	$205.30	$205.30
Purchase #5	$99.34	13.481%	$112.732	$112.73	$112.75	$112.70
Purchase #6	$91.81	10.263%	$101.2325	$101.23	$101.25	$101.20
Purchase #7	$66.48	9.632%	$72.8834	$72.88	$72.90	$72.90
7 purchase totals =	$1,059.29		$1,149.8669	$1,149.86	$1,149.90	$1,149.90