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 $229.55   11.401%   $255.721   $255.72   $255.70   $255.70  
  Purchase #2 $54.92   12.356%   $61.7059   $61.71   $61.70   $61.70  
  Purchase #3 $167.38   12.197%   $187.7953   $187.80   $187.80   $187.80  
  Purchase #4 $59.35   5.611%   $62.6801   $62.68   $62.70   $62.70  
  Purchase #5 $226.55   11.228%   $251.987   $251.99   $252.00   $252.00  
  Purchase #6 $247.63   13.498%   $281.0551   $281.06   $281.05   $281.10  
  Purchase #7 $207.46   9.655%   $227.4903   $227.49   $227.50   $227.50  
  7 purchase totals = $1,192.84       $1,328.4347   $1,328.45   $1,328.45   $1,328.50