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	$76.74	13.135%	$86.8198	$86.82	$86.80	$86.80
Purchase #2	$203.46	6.611%	$216.9107	$216.91	$216.90	$216.90
Purchase #3	$238.31	12.807%	$268.8304	$268.83	$268.85	$268.80
Purchase #4	$64.64	10.724%	$71.572	$71.57	$71.55	$71.60
Purchase #5	$84.43	3.457%	$87.3487	$87.35	$87.35	$87.30
Purchase #6	$25.25	11.409%	$28.1308	$28.13	$28.15	$28.10
Purchase #7	$101.96	9.360%	$111.5035	$111.50	$111.50	$111.50
7 purchase totals =	$794.79		$871.1159	$871.11	$871.10	$871.00