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 $243.57   6.161%   $258.5763   $258.58   $258.60   $258.60  
  Purchase #2 $79.56   10.473%   $87.8923   $87.89   $87.90   $87.90  
  Purchase #3 $86.72   9.544%   $94.9966   $95.00   $95.00   $95.00  
  Purchase #4 $206.46   10.859%   $228.8795   $228.88   $228.90   $228.90  
  Purchase #5 $132.56   8.658%   $144.037   $144.04   $144.05   $144.00  
  Purchase #6 $188.35   6.721%   $201.009   $201.01   $201.00   $201.00  
  Purchase #7 $34.54   11.667%   $38.5698   $38.57   $38.55   $38.60  
  7 purchase totals = $971.76       $1,053.9605   $1,053.97   $1,054.00   $1,054.00