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	$245.97	9.279%	$268.7936	$268.79	$268.80	$268.80
Purchase #2	$221.45	13.215%	$250.7146	$250.71	$250.70	$250.70
Purchase #3	$30.64	9.820%	$33.6488	$33.65	$33.65	$33.60
Purchase #4	$109.88	12.793%	$123.9369	$123.94	$123.95	$123.90
Purchase #5	$104.27	9.259%	$113.9244	$113.92	$113.90	$113.90
Purchase #6	$93.46	6.445%	$99.4835	$99.48	$99.50	$99.50
Purchase #7	$119.31	13.268%	$135.1401	$135.14	$135.15	$135.10
7 purchase totals =	$924.98		$1,025.6419	$1,025.63	$1,025.65	$1,025.50