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	$28.89	7.700%	$31.1145	$31.11	$31.10	$31.10
Purchase #2	$51.90	7.774%	$55.9347	$55.93	$55.95	$55.90
Purchase #3	$20.89	4.802%	$21.8931	$21.89	$21.90	$21.90
Purchase #4	$38.27	9.801%	$42.0208	$42.02	$42.00	$42.00
Purchase #5	$129.33	4.454%	$135.0904	$135.09	$135.10	$135.10
Purchase #6	$167.40	6.844%	$178.8569	$178.86	$178.85	$178.90
Purchase #7	$245.56	7.568%	$264.144	$264.14	$264.15	$264.10
7 purchase totals =	$682.24		$729.0544	$729.04	$729.05	$729.00