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	$30.85	7.319%	$33.1079	$33.11	$33.10	$33.10
Purchase #2	$42.89	4.604%	$44.8647	$44.86	$44.85	$44.90
Purchase #3	$49.46	5.810%	$52.3336	$52.33	$52.35	$52.30
Purchase #4	$116.73	3.172%	$120.4327	$120.43	$120.45	$120.40
Purchase #5	$209.30	12.142%	$234.7132	$234.71	$234.70	$234.70
Purchase #6	$78.78	12.658%	$88.752	$88.75	$88.75	$88.80
Purchase #7	$7.37	7.774%	$7.9429	$7.94	$7.95	$7.90
7 purchase totals =	$535.38		$582.1470	$582.13	$582.15	$582.10