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	$240.81	5.447%	$253.9269	$253.93	$253.95	$253.90
Purchase #2	$221.40	13.318%	$250.8861	$250.89	$250.90	$250.90
Purchase #3	$27.90	9.751%	$30.6205	$30.62	$30.60	$30.60
Purchase #4	$40.81	7.483%	$43.8638	$43.86	$43.85	$43.90
Purchase #5	$100.73	8.624%	$109.417	$109.42	$109.40	$109.40
Purchase #6	$77.82	9.596%	$85.2876	$85.29	$85.30	$85.30
Purchase #7	$201.36	5.232%	$211.8952	$211.90	$211.90	$211.90
7 purchase totals =	$910.83		$985.8971	$985.91	$985.90	$985.90