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	$85.26	7.577%	$91.7202	$91.72	$91.70	$91.70
Purchase #2	$112.88	11.118%	$125.43	$125.43	$125.45	$125.40
Purchase #3	$98.80	10.689%	$109.3607	$109.36	$109.35	$109.40
Purchase #4	$57.89	3.122%	$59.6973	$59.70	$59.70	$59.70
Purchase #5	$28.31	8.627%	$30.7523	$30.75	$30.75	$30.80
Purchase #6	$10.72	5.736%	$11.3349	$11.33	$11.35	$11.30
Purchase #7	$47.52	9.198%	$51.8909	$51.89	$51.90	$51.90
7 purchase totals =	$441.38		$480.1863	$480.18	$480.20	$480.20