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	$245.35	11.273%	$273.0083	$273.01	$273.00	$273.00
Purchase #2	$112.98	4.343%	$117.8867	$117.89	$117.90	$117.90
Purchase #3	$7.71	7.862%	$8.3162	$8.32	$8.30	$8.30
Purchase #4	$46.59	7.359%	$50.0186	$50.02	$50.00	$50.00
Purchase #5	$248.77	6.248%	$264.3131	$264.31	$264.30	$264.30
Purchase #6	$72.76	12.855%	$82.1133	$82.11	$82.10	$82.10
Purchase #7	$133.73	12.873%	$150.9451	$150.95	$150.95	$150.90
7 purchase totals =	$867.89		$946.6013	$946.61	$946.55	$946.50