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	$96.33	13.384%	$109.2228	$109.22	$109.20	$109.20
Purchase #2	$191.67	6.600%	$204.3202	$204.32	$204.30	$204.30
Purchase #3	$199.31	8.104%	$215.4621	$215.46	$215.45	$215.50
Purchase #4	$224.79	13.659%	$255.4941	$255.49	$255.50	$255.50
Purchase #5	$174.59	11.630%	$194.8948	$194.89	$194.90	$194.90
Purchase #6	$170.33	11.699%	$190.2569	$190.26	$190.25	$190.30
Purchase #7	$75.67	5.322%	$79.6972	$79.70	$79.70	$79.70
7 purchase totals =	$1,132.69		$1,249.3481	$1,249.34	$1,249.30	$1,249.40