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	$88.57	13.735%	$100.7351	$100.74	$100.75	$100.70
Purchase #2	$148.97	9.322%	$162.857	$162.86	$162.85	$162.90
Purchase #3	$216.84	5.788%	$229.3907	$229.39	$229.40	$229.40
Purchase #4	$118.34	8.477%	$128.3717	$128.37	$128.35	$128.40
Purchase #5	$250.76	9.484%	$274.5421	$274.54	$274.55	$274.50
Purchase #6	$115.36	11.313%	$128.4107	$128.41	$128.40	$128.40
Purchase #7	$177.73	7.479%	$191.0224	$191.02	$191.00	$191.00
7 purchase totals =	$1,116.57		$1,215.3297	$1,215.33	$1,215.30	$1,215.30