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	$42.28	7.693%	$45.5326	$45.53	$45.55	$45.50
Purchase #2	$77.86	7.132%	$83.413	$83.41	$83.40	$83.40
Purchase #3	$85.33	6.238%	$90.6529	$90.65	$90.65	$90.70
Purchase #4	$43.55	11.459%	$48.5404	$48.54	$48.55	$48.50
Purchase #5	$5.99	10.304%	$6.6072	$6.61	$6.60	$6.60
Purchase #6	$189.76	12.360%	$213.2143	$213.21	$213.20	$213.20
Purchase #7	$69.65	3.180%	$71.8649	$71.86	$71.85	$71.90
7 purchase totals =	$514.42		$559.8253	$559.81	$559.80	$559.80