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	$180.59	3.591%	$187.075	$187.08	$187.10	$187.10
Purchase #2	$103.79	9.371%	$113.5162	$113.52	$113.50	$113.50
Purchase #3	$206.46	8.220%	$223.431	$223.43	$223.45	$223.40
Purchase #4	$104.78	9.645%	$114.886	$114.89	$114.90	$114.90
Purchase #5	$242.90	4.332%	$253.4224	$253.42	$253.40	$253.40
Purchase #6	$211.80	4.289%	$220.8841	$220.88	$220.90	$220.90
Purchase #7	$150.83	9.556%	$165.2433	$165.24	$165.25	$165.20
7 purchase totals =	$1,201.15		$1,278.4580	$1,278.46	$1,278.50	$1,278.40