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	$83.39	10.643%	$92.2652	$92.27	$92.25	$92.30
Purchase #2	$76.46	11.745%	$85.4402	$85.44	$85.45	$85.40
Purchase #3	$227.68	10.190%	$250.8806	$250.88	$250.90	$250.90
Purchase #4	$20.59	4.309%	$21.4772	$21.48	$21.50	$21.50
Purchase #5	$196.32	6.676%	$209.4263	$209.43	$209.45	$209.40
Purchase #6	$176.48	10.782%	$195.5081	$195.51	$195.50	$195.50
Purchase #7	$42.95	6.843%	$45.8891	$45.89	$45.90	$45.90
7 purchase totals =	$823.87		$900.8867	$900.90	$900.95	$900.90