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 $220.85   5.410%   $232.798   $232.80   $232.80   $232.80  
  Purchase #2 $119.59   3.335%   $123.5783   $123.58   $123.60   $123.60  
  Purchase #3 $230.63   3.500%   $238.7021   $238.70   $238.70   $238.70  
  Purchase #4 $39.70   12.231%   $44.5557   $44.56   $44.55   $44.60  
  Purchase #5 $136.60   13.189%   $154.6162   $154.62   $154.60   $154.60  
  Purchase #6 $124.60   8.183%   $134.796   $134.80   $134.80   $134.80  
  Purchase #7 $67.80   9.395%   $74.1698   $74.17   $74.15   $74.20  
  7 purchase totals = $939.77       $1,003.2161   $1,003.23   $1,003.20   $1,003.30