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	$70.75	11.569%	$78.9351	$78.94	$78.95	$78.90
Purchase #2	$205.98	7.719%	$221.8796	$221.88	$221.90	$221.90
Purchase #3	$86.39	4.620%	$90.3812	$90.38	$90.40	$90.40
Purchase #4	$80.36	12.133%	$90.1101	$90.11	$90.10	$90.10
Purchase #5	$192.39	5.505%	$202.9811	$202.98	$203.00	$203.00
Purchase #6	$222.38	4.654%	$232.7296	$232.73	$232.75	$232.70
Purchase #7	$173.26	3.406%	$179.1612	$179.16	$179.15	$179.20
7 purchase totals =	$1,031.51		$1,096.1779	$1,096.18	$1,096.25	$1,096.20