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	$244.49	11.745%	$273.2054	$273.21	$273.20	$273.20
Purchase #2	$58.33	4.206%	$60.7834	$60.78	$60.80	$60.80
Purchase #3	$226.67	3.181%	$233.8804	$233.88	$233.90	$233.90
Purchase #4	$225.70	5.410%	$237.9104	$237.91	$237.90	$237.90
Purchase #5	$156.29	7.691%	$168.3103	$168.31	$168.30	$168.30
Purchase #6	$210.59	6.119%	$223.476	$223.48	$223.50	$223.50
Purchase #7	$156.76	3.756%	$162.6479	$162.65	$162.65	$162.60
7 purchase totals =	$1,278.83		$1,360.2138	$1,360.22	$1,360.25	$1,360.20