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	$200.79	13.459%	$227.8143	$227.81	$227.80	$227.80
Purchase #2	$175.83	5.478%	$185.462	$185.46	$185.45	$185.50
Purchase #3	$234.96	9.580%	$257.4692	$257.47	$257.45	$257.50
Purchase #4	$30.71	7.112%	$32.8941	$32.89	$32.90	$32.90
Purchase #5	$135.66	3.770%	$140.7744	$140.77	$140.75	$140.80
Purchase #6	$12.58	10.270%	$13.872	$13.87	$13.85	$13.90
Purchase #7	$31.78	11.505%	$35.4363	$35.44	$35.45	$35.40
7 purchase totals =	$822.31		$893.7223	$893.71	$893.65	$893.80