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	$33.59	11.133%	$37.3296	$37.33	$37.35	$37.30
Purchase #2	$131.48	12.210%	$147.5337	$147.53	$147.55	$147.50
Purchase #3	$52.76	12.279%	$59.2384	$59.24	$59.25	$59.20
Purchase #4	$20.95	8.173%	$22.6622	$22.66	$22.65	$22.70
Purchase #5	$50.92	13.184%	$57.6333	$57.63	$57.65	$57.60
Purchase #6	$40.38	9.568%	$44.2436	$44.24	$44.25	$44.20
Purchase #7	$210.96	10.190%	$232.4568	$232.46	$232.45	$232.50
7 purchase totals =	$541.04		$601.0976	$601.09	$601.15	$601.00