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 $227.56   11.154%   $252.942   $252.94   $252.95   $252.90  
  Purchase #2 $33.55   4.514%   $35.0644   $35.06   $35.05   $35.10  
  Purchase #3 $27.32   6.738%   $29.1608   $29.16   $29.15   $29.20  
  Purchase #4 $213.86   6.762%   $228.3212   $228.32   $228.30   $228.30  
  Purchase #5 $162.68   13.631%   $184.8549   $184.85   $184.85   $184.90  
  Purchase #6 $103.34   4.334%   $107.8188   $107.82   $107.80   $107.80  
  Purchase #7 $212.64   8.725%   $231.1928   $231.19   $231.20   $231.20  
  7 purchase totals = $980.95       $1,069.3549   $1,069.34   $1,069.30   $1,069.40