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 $101.94   8.530%   $110.6355   $110.64   $110.65   $110.60  
  Purchase #2 $226.74   10.155%   $249.7654   $249.77   $249.75   $249.80  
  Purchase #3 $205.49   8.369%   $222.6875   $222.69   $222.70   $222.70  
  Purchase #4 $51.54   6.352%   $54.8138   $54.81   $54.80   $54.80  
  Purchase #5 $236.35   4.317%   $246.5532   $246.55   $246.55   $246.60  
  Purchase #6 $179.26   12.433%   $201.5474   $201.55   $201.55   $201.50  
  Purchase #7 $28.63   13.706%   $32.554   $32.55   $32.55   $32.60  
  7 purchase totals = $1,029.95       $1,118.5568   $1,118.56   $1,118.55   $1,118.60