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	$135.84	5.536%	$143.3601	$143.36	$143.35	$143.40
Purchase #2	$200.70	11.710%	$224.202	$224.20	$224.20	$224.20
Purchase #3	$64.90	12.709%	$73.1481	$73.15	$73.15	$73.10
Purchase #4	$54.34	9.572%	$59.5414	$59.54	$59.55	$59.50
Purchase #5	$18.46	6.154%	$19.596	$19.60	$19.60	$19.60
Purchase #6	$71.47	6.505%	$76.1191	$76.12	$76.10	$76.10
Purchase #7	$64.98	11.665%	$72.5599	$72.56	$72.55	$72.60
7 purchase totals =	$610.69		$668.5266	$668.53	$668.50	$668.50