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	$14.48	5.439%	$15.2676	$15.27	$15.25	$15.30
Purchase #2	$106.41	5.166%	$111.9071	$111.91	$111.90	$111.90
Purchase #3	$222.89	6.688%	$237.7969	$237.80	$237.80	$237.80
Purchase #4	$242.36	12.786%	$273.3481	$273.35	$273.35	$273.30
Purchase #5	$207.94	7.454%	$223.4398	$223.44	$223.45	$223.40
Purchase #6	$33.34	12.221%	$37.4145	$37.41	$37.40	$37.40
Purchase #7	$79.45	4.789%	$83.2549	$83.25	$83.25	$83.30
7 purchase totals =	$906.87		$982.4289	$982.43	$982.40	$982.40