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	$245.47	11.613%	$273.9764	$273.98	$274.00	$274.00
Purchase #2	$195.79	12.816%	$220.8824	$220.88	$220.90	$220.90
Purchase #3	$85.67	12.268%	$96.18	$96.18	$96.20	$96.20
Purchase #4	$142.91	5.119%	$150.2256	$150.23	$150.25	$150.20
Purchase #5	$78.83	12.344%	$88.5608	$88.56	$88.55	$88.60
Purchase #6	$59.86	12.488%	$67.3353	$67.34	$67.35	$67.30
Purchase #7	$38.58	6.116%	$40.9396	$40.94	$40.95	$40.90
7 purchase totals =	$847.11		$938.1001	$938.11	$938.20	$938.10