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 $118.46   3.832%   $122.9994   $123.00   $123.00   $123.00  
  Purchase #2 $22.79   9.432%   $24.9396   $24.94   $24.95   $24.90  
  Purchase #3 $34.47   13.746%   $39.2082   $39.21   $39.20   $39.20  
  Purchase #4 $235.53   13.849%   $268.1485   $268.15   $268.15   $268.10  
  Purchase #5 $125.79   9.721%   $138.018   $138.02   $138.00   $138.00  
  Purchase #6 $246.49   4.233%   $256.9239   $256.92   $256.90   $256.90  
  Purchase #7 $170.42   7.592%   $183.3583   $183.36   $183.35   $183.40  
  7 purchase totals = $953.95       $1,033.5959   $1,033.60   $1,033.55   $1,033.50