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 $146.58   9.608%   $160.6634   $160.66   $160.65   $160.70  
  Purchase #2 $124.42   4.192%   $129.6357   $129.64   $129.65   $129.60  
  Purchase #3 $22.35   3.653%   $23.1664   $23.17   $23.15   $23.20  
  Purchase #4 $241.67   3.695%   $250.5997   $250.60   $250.60   $250.60  
  Purchase #5 $163.91   5.353%   $172.6841   $172.68   $172.70   $172.70  
  Purchase #6 $56.58   5.143%   $59.4899   $59.49   $59.50   $59.50  
  Purchase #7 $218.64   4.398%   $228.2558   $228.26   $228.25   $228.30  
  7 purchase totals = $974.15       $1,024.4950   $1,024.50   $1,024.50   $1,024.60