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	$250.63	9.817%	$275.2343	$275.23	$275.25	$275.20
Purchase #2	$236.53	11.807%	$264.4571	$264.46	$264.45	$264.50
Purchase #3	$57.45	3.144%	$59.2562	$59.26	$59.25	$59.30
Purchase #4	$125.78	5.120%	$132.2199	$132.22	$132.20	$132.20
Purchase #5	$7.66	7.847%	$8.2611	$8.26	$8.25	$8.30
Purchase #6	$125.87	10.281%	$138.8107	$138.81	$138.80	$138.80
Purchase #7	$67.38	7.664%	$72.544	$72.54	$72.55	$72.50
7 purchase totals =	$871.30		$950.7833	$950.78	$950.75	$950.80