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	$120.66	9.365%	$131.9598	$131.96	$131.95	$132.00
Purchase #2	$122.61	4.378%	$127.9779	$127.98	$128.00	$128.00
Purchase #3	$192.76	13.821%	$219.4014	$219.40	$219.40	$219.40
Purchase #4	$5.35	9.319%	$5.8486	$5.85	$5.85	$5.80
Purchase #5	$99.47	12.330%	$111.7347	$111.73	$111.75	$111.70
Purchase #6	$210.90	13.872%	$240.156	$240.16	$240.15	$240.20
Purchase #7	$109.46	13.818%	$124.5852	$124.59	$124.60	$124.60
7 purchase totals =	$861.21		$961.6636	$961.67	$961.70	$961.70