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	$85.34	10.681%	$94.4552	$94.46	$94.45	$94.50
Purchase #2	$199.99	5.432%	$210.8535	$210.85	$210.85	$210.90
Purchase #3	$170.38	8.846%	$185.4518	$185.45	$185.45	$185.50
Purchase #4	$93.45	6.829%	$99.8317	$99.83	$99.85	$99.80
Purchase #5	$116.42	11.676%	$130.0132	$130.01	$130.00	$130.00
Purchase #6	$159.80	12.282%	$179.4266	$179.43	$179.45	$179.40
Purchase #7	$22.71	7.660%	$24.4496	$24.45	$24.45	$24.40
7 purchase totals =	$848.09		$924.4816	$924.48	$924.50	$924.50