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 $98.97   8.623%   $107.5042   $107.50   $107.50   $107.50  
  Purchase #2 $163.81   7.365%   $175.8746   $175.87   $175.85   $175.90  
  Purchase #3 $40.51   12.681%   $45.6471   $45.65   $45.65   $45.60  
  Purchase #4 $232.64   8.424%   $252.2376   $252.24   $252.25   $252.20  
  Purchase #5 $164.59   6.515%   $175.313   $175.31   $175.30   $175.30  
  Purchase #6 $247.57   7.202%   $265.4   $265.40   $265.40   $265.40  
  Purchase #7 $225.98   8.538%   $245.2742   $245.27   $245.25   $245.30  
  7 purchase totals = $1,174.07       $1,267.2507   $1,267.24   $1,267.20   $1,267.20