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 $63.54   7.263%   $68.1549   $68.15   $68.15   $68.20  
  Purchase #2 $211.84   10.286%   $233.6299   $233.63   $233.65   $233.60  
  Purchase #3 $241.65   11.815%   $270.2009   $270.20   $270.20   $270.20  
  Purchase #4 $133.66   12.423%   $150.2646   $150.26   $150.25   $150.30  
  Purchase #5 $127.42   7.868%   $137.4454   $137.45   $137.45   $137.40  
  Purchase #6 $219.91   12.293%   $246.9435   $246.94   $246.95   $246.90  
  Purchase #7 $31.69   10.116%   $34.8958   $34.90   $34.90   $34.90  
  7 purchase totals = $1,029.71       $1,141.5350   $1,141.53   $1,141.55   $1,141.50