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	$90.75	13.374%	$102.8869	$102.89	$102.90	$102.90
Purchase #2	$101.54	3.174%	$104.7629	$104.76	$104.75	$104.80
Purchase #3	$185.99	6.634%	$198.3286	$198.33	$198.35	$198.30
Purchase #4	$84.98	5.618%	$89.7542	$89.75	$89.75	$89.80
Purchase #5	$142.92	5.212%	$150.369	$150.37	$150.35	$150.40
Purchase #6	$37.80	7.635%	$40.686	$40.69	$40.70	$40.70
Purchase #7	$134.86	3.148%	$139.1054	$139.11	$139.10	$139.10
7 purchase totals =	$778.84		$825.8930	$825.90	$825.90	$826.00