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	$28.27	11.371%	$31.4846	$31.48	$31.50	$31.50
Purchase #2	$27.99	12.313%	$31.4364	$31.44	$31.45	$31.40
Purchase #3	$69.73	11.400%	$77.6792	$77.68	$77.70	$77.70
Purchase #4	$192.32	3.415%	$198.8877	$198.89	$198.90	$198.90
Purchase #5	$150.47	7.290%	$161.4393	$161.44	$161.45	$161.40
Purchase #6	$67.33	12.165%	$75.5207	$75.52	$75.50	$75.50
Purchase #7	$83.53	9.578%	$91.5305	$91.53	$91.55	$91.50
7 purchase totals =	$619.64		$667.9784	$667.98	$668.05	$667.90