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	$48.31	6.330%	$51.368	$51.37	$51.35	$51.40
Purchase #2	$34.63	5.284%	$36.4598	$36.46	$36.45	$36.50
Purchase #3	$249.91	12.407%	$280.9163	$280.92	$280.90	$280.90
Purchase #4	$149.50	3.834%	$155.2318	$155.23	$155.25	$155.20
Purchase #5	$143.41	13.259%	$162.4247	$162.42	$162.40	$162.40
Purchase #6	$246.38	12.782%	$277.8723	$277.87	$277.85	$277.90
Purchase #7	$55.81	6.600%	$59.4935	$59.49	$59.50	$59.50
7 purchase totals =	$927.95		$1,023.7664	$1,023.76	$1,023.70	$1,023.80