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	$189.71	11.170%	$210.9006	$210.90	$210.90	$210.90
Purchase #2	$16.73	13.193%	$18.9372	$18.94	$18.95	$18.90
Purchase #3	$26.28	8.206%	$28.4365	$28.44	$28.45	$28.40
Purchase #4	$186.25	5.408%	$196.3224	$196.32	$196.30	$196.30
Purchase #5	$84.81	6.596%	$90.4041	$90.40	$90.40	$90.40
Purchase #6	$102.93	10.291%	$113.5225	$113.52	$113.50	$113.50
Purchase #7	$242.61	12.656%	$273.3147	$273.31	$273.30	$273.30
7 purchase totals =	$849.32		$931.8380	$931.83	$931.80	$931.70