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	$102.88	6.155%	$109.2123	$109.21	$109.20	$109.20
Purchase #2	$140.32	7.483%	$150.8201	$150.82	$150.80	$150.80
Purchase #3	$30.33	9.562%	$33.2302	$33.23	$33.25	$33.20
Purchase #4	$143.25	9.374%	$156.6783	$156.68	$156.70	$156.70
Purchase #5	$55.55	7.110%	$59.4996	$59.50	$59.50	$59.50
Purchase #6	$198.56	11.709%	$221.8094	$221.81	$221.80	$221.80
Purchase #7	$189.25	7.267%	$203.0028	$203.00	$203.00	$203.00
7 purchase totals =	$860.14		$934.2527	$934.25	$934.25	$934.20