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 $88.65   5.611%   $93.6242   $93.62   $93.60   $93.60  
  Purchase #2 $212.48   4.828%   $222.7385   $222.74   $222.75   $222.70  
  Purchase #3 $33.26   7.852%   $35.8716   $35.87   $35.85   $35.90  
  Purchase #4 $11.43   10.533%   $12.6339   $12.63   $12.65   $12.60  
  Purchase #5 $79.47   6.374%   $84.5354   $84.54   $84.55   $84.50  
  Purchase #6 $180.77   13.169%   $204.5756   $204.58   $204.60   $204.60  
  Purchase #7 $122.75   8.675%   $133.3986   $133.40   $133.40   $133.40  
  7 purchase totals = $728.81       $787.3778   $787.38   $787.40   $787.30