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	$41.49	8.834%	$45.1552	$45.16	$45.15	$45.20
Purchase #2	$43.32	5.297%	$45.6147	$45.61	$45.60	$45.60
Purchase #3	$155.94	8.588%	$169.3321	$169.33	$169.35	$169.30
Purchase #4	$225.67	6.618%	$240.6048	$240.60	$240.60	$240.60
Purchase #5	$65.31	10.105%	$71.9096	$71.91	$71.90	$71.90
Purchase #6	$250.46	10.272%	$276.1873	$276.19	$276.20	$276.20
Purchase #7	$65.46	12.558%	$73.6805	$73.68	$73.70	$73.70
7 purchase totals =	$847.65		$922.4842	$922.48	$922.50	$922.50