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 $231.93   13.218%   $262.5865   $262.59   $262.60   $262.60  
  Purchase #2 $210.58   13.814%   $239.6695   $239.67   $239.65   $239.70  
  Purchase #3 $207.47   10.639%   $229.5427   $229.54   $229.55   $229.50  
  Purchase #4 $216.77   9.210%   $236.7345   $236.73   $236.75   $236.70  
  Purchase #5 $50.91   11.861%   $56.9484   $56.95   $56.95   $56.90  
  Purchase #6 $129.36   3.595%   $134.0105   $134.01   $134.00   $134.00  
  Purchase #7 $109.85   9.411%   $120.188   $120.19   $120.20   $120.20  
  7 purchase totals = $1,156.87       $1,279.6801   $1,279.68   $1,279.70   $1,279.60