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	$128.54	5.282%	$135.3295	$135.33	$135.35	$135.30
Purchase #2	$201.61	13.872%	$229.5773	$229.58	$229.60	$229.60
Purchase #3	$153.56	7.822%	$165.5715	$165.57	$165.55	$165.60
Purchase #4	$150.61	9.803%	$165.3743	$165.37	$165.35	$165.40
Purchase #5	$122.36	5.108%	$128.6101	$128.61	$128.60	$128.60
Purchase #6	$88.41	11.452%	$98.5347	$98.53	$98.55	$98.50
Purchase #7	$98.97	10.382%	$109.2451	$109.25	$109.25	$109.20
7 purchase totals =	$944.06		$1,032.2425	$1,032.24	$1,032.25	$1,032.20