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	$85.41	6.412%	$90.8865	$90.89	$90.90	$90.90
Purchase #2	$191.82	9.358%	$209.7705	$209.77	$209.75	$209.80
Purchase #3	$249.54	9.517%	$273.2887	$273.29	$273.30	$273.30
Purchase #4	$232.74	5.605%	$245.7851	$245.79	$245.80	$245.80
Purchase #5	$187.76	10.412%	$207.3096	$207.31	$207.30	$207.30
Purchase #6	$40.86	4.644%	$42.7575	$42.76	$42.75	$42.80
Purchase #7	$117.92	11.477%	$131.4537	$131.45	$131.45	$131.50
7 purchase totals =	$1,106.05		$1,201.2516	$1,201.26	$1,201.25	$1,201.40