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	$9.79	5.648%	$10.3429	$10.34	$10.35	$10.30
Purchase #2	$155.36	6.844%	$165.9928	$165.99	$166.00	$166.00
Purchase #3	$79.78	11.681%	$89.0991	$89.10	$89.10	$89.10
Purchase #4	$155.48	7.702%	$167.4551	$167.46	$167.45	$167.50
Purchase #5	$39.78	6.440%	$42.3418	$42.34	$42.35	$42.30
Purchase #6	$78.98	4.661%	$82.6613	$82.66	$82.65	$82.70
Purchase #7	$163.85	11.141%	$182.1045	$182.10	$182.10	$182.10
7 purchase totals =	$683.02		$739.9975	$739.99	$740.00	$740.00