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 $120.58   5.296%   $126.9659   $126.97   $126.95   $127.00  
  Purchase #2 $72.32   3.777%   $75.0515   $75.05   $75.05   $75.10  
  Purchase #3 $118.80   6.282%   $126.263   $126.26   $126.25   $126.30  
  Purchase #4 $10.76   13.632%   $12.2268   $12.23   $12.25   $12.20  
  Purchase #5 $227.28   9.454%   $248.7671   $248.77   $248.75   $248.80  
  Purchase #6 $58.49   10.827%   $64.8227   $64.82   $64.80   $64.80  
  Purchase #7 $41.99   6.843%   $44.8634   $44.86   $44.85   $44.90  
  7 purchase totals = $650.22       $698.9604   $698.96   $698.90   $699.10