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 $24.26   9.544%   $26.5754   $26.58   $26.60   $26.60  
  Purchase #2 $226.77   12.652%   $255.4609   $255.46   $255.45   $255.50  
  Purchase #3 $111.31   9.206%   $121.5572   $121.56   $121.55   $121.60  
  Purchase #4 $17.67   11.609%   $19.7213   $19.72   $19.70   $19.70  
  Purchase #5 $172.35   12.119%   $193.2371   $193.24   $193.25   $193.20  
  Purchase #6 $248.98   10.658%   $275.5163   $275.52   $275.50   $275.50  
  Purchase #7 $185.65   13.167%   $210.0945   $210.09   $210.10   $210.10  
  7 purchase totals = $986.99       $1,102.1627   $1,102.17   $1,102.15   $1,102.20