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	$39.26	11.793%	$43.8899	$43.89	$43.90	$43.90
Purchase #2	$78.56	10.610%	$86.8952	$86.90	$86.90	$86.90
Purchase #3	$164.99	3.222%	$170.306	$170.31	$170.30	$170.30
Purchase #4	$90.67	8.427%	$98.3108	$98.31	$98.30	$98.30
Purchase #5	$142.47	8.556%	$154.6597	$154.66	$154.65	$154.70
Purchase #6	$215.47	13.204%	$243.9207	$243.92	$243.90	$243.90
Purchase #7	$103.36	9.449%	$113.1265	$113.13	$113.15	$113.10
7 purchase totals =	$834.78		$911.1088	$911.12	$911.10	$911.10