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	$86.25	12.358%	$96.9088	$96.91	$96.90	$96.90
Purchase #2	$81.33	10.645%	$89.9876	$89.99	$90.00	$90.00
Purchase #3	$177.36	7.397%	$190.4793	$190.48	$190.50	$190.50
Purchase #4	$115.74	13.253%	$131.079	$131.08	$131.10	$131.10
Purchase #5	$240.88	12.226%	$270.33	$270.33	$270.35	$270.30
Purchase #6	$107.47	3.537%	$111.2712	$111.27	$111.25	$111.30
Purchase #7	$66.86	9.608%	$73.2839	$73.28	$73.30	$73.30
7 purchase totals =	$875.89		$963.3398	$963.34	$963.40	$963.40