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	$73.56	6.729%	$78.5099	$78.51	$78.50	$78.50
Purchase #2	$129.42	9.372%	$141.5492	$141.55	$141.55	$141.50
Purchase #3	$202.87	12.122%	$227.4619	$227.46	$227.45	$227.50
Purchase #4	$194.86	9.591%	$213.549	$213.55	$213.55	$213.50
Purchase #5	$13.73	3.454%	$14.2042	$14.20	$14.20	$14.20
Purchase #6	$177.54	3.815%	$184.3132	$184.31	$184.30	$184.30
Purchase #7	$121.92	12.650%	$137.3429	$137.34	$137.35	$137.30
7 purchase totals =	$913.90		$996.9303	$996.92	$996.90	$996.80