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 $141.53   12.813%   $159.6642   $159.66   $159.65   $159.70  
  Purchase #2 $91.63   5.126%   $96.327   $96.33   $96.35   $96.30  
  Purchase #3 $151.76   4.841%   $159.1067   $159.11   $159.10   $159.10  
  Purchase #4 $241.25   11.485%   $268.9576   $268.96   $268.95   $269.00  
  Purchase #5 $105.47   5.608%   $111.3848   $111.38   $111.40   $111.40  
  Purchase #6 $99.80   4.653%   $104.4437   $104.44   $104.45   $104.40  
  Purchase #7 $188.65   9.294%   $206.1831   $206.18   $206.20   $206.20  
  7 purchase totals = $1,020.09       $1,106.0671   $1,106.06   $1,106.10   $1,106.10