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 $66.66   13.646%   $75.7564   $75.76   $75.75   $75.80  
  Purchase #2 $49.74   13.456%   $56.433   $56.43   $56.45   $56.40  
  Purchase #3 $103.43   4.154%   $107.7265   $107.73   $107.75   $107.70  
  Purchase #4 $84.74   9.619%   $92.8911   $92.89   $92.90   $92.90  
  Purchase #5 $186.49   5.426%   $196.6089   $196.61   $196.60   $196.60  
  Purchase #6 $184.32   10.617%   $203.8893   $203.89   $203.90   $203.90  
  Purchase #7 $33.84   6.835%   $36.153   $36.15   $36.15   $36.20  
  7 purchase totals = $709.22       $769.4582   $769.46   $769.50   $769.50