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 $22.74   8.487%   $24.6699   $24.67   $24.65   $24.70  
  Purchase #2 $155.45   10.484%   $171.7474   $171.75   $171.75   $171.70  
  Purchase #3 $157.78   11.283%   $175.5823   $175.58   $175.60   $175.60  
  Purchase #4 $116.29   11.525%   $129.6924   $129.69   $129.70   $129.70  
  Purchase #5 $193.64   3.830%   $201.0564   $201.06   $201.05   $201.10  
  Purchase #6 $169.53   8.320%   $183.6349   $183.63   $183.65   $183.60  
  Purchase #7 $127.43   9.548%   $139.597   $139.60   $139.60   $139.60  
  7 purchase totals = $942.86       $1,025.9803   $1,025.98   $1,026.00   $1,026.00