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	$86.86	4.855%	$91.0771	$91.08	$91.10	$91.10
Purchase #2	$240.99	12.417%	$270.9137	$270.91	$270.90	$270.90
Purchase #3	$70.54	11.842%	$78.8933	$78.89	$78.90	$78.90
Purchase #4	$82.45	11.241%	$91.7182	$91.72	$91.70	$91.70
Purchase #5	$57.26	12.315%	$64.3116	$64.31	$64.30	$64.30
Purchase #6	$203.98	11.767%	$227.9823	$227.98	$228.00	$228.00
Purchase #7	$178.76	3.555%	$185.1149	$185.11	$185.10	$185.10
7 purchase totals =	$920.84		$1,010.0111	$1,010.00	$1,010.00	$1,010.00