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	$200.51	11.454%	$223.4764	$223.48	$223.50	$223.50
Purchase #2	$130.88	8.790%	$142.3844	$142.38	$142.40	$142.40
Purchase #3	$206.91	11.807%	$231.3399	$231.34	$231.35	$231.30
Purchase #4	$169.60	12.681%	$191.107	$191.11	$191.10	$191.10
Purchase #5	$59.58	3.808%	$61.8488	$61.85	$61.85	$61.80
Purchase #6	$71.89	11.543%	$80.1883	$80.19	$80.20	$80.20
Purchase #7	$70.80	12.162%	$79.4107	$79.41	$79.40	$79.40
7 purchase totals =	$910.17		$1,009.7555	$1,009.76	$1,009.80	$1,009.70