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	$18.57	10.475%	$20.5152	$20.52	$20.50	$20.50
Purchase #2	$55.36	8.280%	$59.9438	$59.94	$59.95	$59.90
Purchase #3	$147.55	8.460%	$160.0327	$160.03	$160.05	$160.00
Purchase #4	$113.84	8.107%	$123.069	$123.07	$123.05	$123.10
Purchase #5	$220.37	7.787%	$237.5302	$237.53	$237.55	$237.50
Purchase #6	$156.76	9.765%	$172.0676	$172.07	$172.05	$172.10
Purchase #7	$64.73	11.366%	$72.0872	$72.09	$72.10	$72.10
7 purchase totals =	$777.18		$845.2457	$845.25	$845.25	$845.20