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 $10.84   5.612%   $11.4483   $11.45   $11.45   $11.40  
  Purchase #2 $250.84   12.200%   $281.4425   $281.44   $281.45   $281.40  
  Purchase #3 $10.29   3.410%   $10.6409   $10.64   $10.65   $10.60  
  Purchase #4 $106.54   6.296%   $113.2478   $113.25   $113.25   $113.20  
  Purchase #5 $129.66   7.285%   $139.1057   $139.11   $139.10   $139.10  
  Purchase #6 $208.80   6.799%   $222.9963   $223.00   $223.00   $223.00  
  Purchase #7 $179.27   5.229%   $188.644   $188.64   $188.65   $188.60  
  7 purchase totals = $896.24       $967.5255   $967.53   $967.55   $967.30