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	$102.73	6.653%	$109.5646	$109.56	$109.55	$109.60
Purchase #2	$90.89	9.596%	$99.6118	$99.61	$99.60	$99.60
Purchase #3	$57.41	11.571%	$64.0529	$64.05	$64.05	$64.10
Purchase #4	$147.30	9.336%	$161.0519	$161.05	$161.05	$161.10
Purchase #5	$184.33	9.707%	$202.2229	$202.22	$202.20	$202.20
Purchase #6	$127.78	10.247%	$140.8736	$140.87	$140.85	$140.90
Purchase #7	$157.86	6.780%	$168.5629	$168.56	$168.55	$168.60
7 purchase totals =	$868.30		$945.9406	$945.92	$945.85	$946.10