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	$92.82	11.416%	$103.4163	$103.42	$103.40	$103.40
Purchase #2	$78.54	5.345%	$82.738	$82.74	$82.75	$82.70
Purchase #3	$240.81	13.518%	$273.3627	$273.36	$273.35	$273.40
Purchase #4	$115.68	13.423%	$131.2077	$131.21	$131.20	$131.20
Purchase #5	$191.80	12.842%	$216.431	$216.43	$216.45	$216.40
Purchase #6	$168.41	12.646%	$189.7071	$189.71	$189.70	$189.70
Purchase #7	$5.69	10.770%	$6.3028	$6.30	$6.30	$6.30
7 purchase totals =	$893.75		$1,003.1656	$1,003.17	$1,003.15	$1,003.10