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	$106.61	12.640%	$120.0855	$120.09	$120.10	$120.10
Purchase #2	$75.48	3.690%	$78.2652	$78.27	$78.25	$78.30
Purchase #3	$48.43	11.282%	$53.8939	$53.89	$53.90	$53.90
Purchase #4	$130.75	7.807%	$140.9577	$140.96	$140.95	$141.00
Purchase #5	$203.39	9.527%	$222.767	$222.77	$222.75	$222.80
Purchase #6	$137.69	11.644%	$153.7226	$153.72	$153.70	$153.70
Purchase #7	$247.53	13.661%	$281.3451	$281.35	$281.35	$281.30
7 purchase totals =	$949.88		$1,051.0370	$1,051.05	$1,051.00	$1,051.10