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	$65.41	12.345%	$73.4849	$73.48	$73.50	$73.50
Purchase #2	$232.36	7.836%	$250.5677	$250.57	$250.55	$250.60
Purchase #3	$7.32	7.623%	$7.878	$7.88	$7.90	$7.90
Purchase #4	$32.26	11.658%	$36.0209	$36.02	$36.00	$36.00
Purchase #5	$238.47	12.267%	$267.7231	$267.72	$267.70	$267.70
Purchase #6	$106.59	4.586%	$111.4782	$111.48	$111.50	$111.50
Purchase #7	$115.94	13.147%	$131.1826	$131.18	$131.20	$131.20
7 purchase totals =	$798.35		$878.3354	$878.33	$878.35	$878.40