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 $60.78   10.521%   $67.1747   $67.17   $67.15   $67.20  
  Purchase #2 $233.74   5.111%   $245.6865   $245.69   $245.70   $245.70  
  Purchase #3 $10.82   10.157%   $11.919   $11.92   $11.90   $11.90  
  Purchase #4 $201.57   8.494%   $218.6914   $218.69   $218.70   $218.70  
  Purchase #5 $171.62   5.832%   $181.6289   $181.63   $181.65   $181.60  
  Purchase #6 $124.92   8.179%   $135.1372   $135.14   $135.15   $135.10  
  Purchase #7 $229.60   13.159%   $259.8131   $259.81   $259.80   $259.80  
  7 purchase totals = $1,033.05       $1,120.0508   $1,120.05   $1,120.05   $1,120.00