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	$125.51	13.596%	$142.5743	$142.57	$142.55	$142.60
Purchase #2	$6.49	3.755%	$6.7337	$6.73	$6.75	$6.70
Purchase #3	$171.54	5.459%	$180.9044	$180.90	$180.90	$180.90
Purchase #4	$37.76	13.731%	$42.9448	$42.94	$42.95	$42.90
Purchase #5	$38.70	3.861%	$40.1942	$40.19	$40.20	$40.20
Purchase #6	$89.45	5.453%	$94.3277	$94.33	$94.35	$94.30
Purchase #7	$231.44	4.430%	$241.6928	$241.69	$241.70	$241.70
7 purchase totals =	$700.89		$749.3719	$749.35	$749.40	$749.30