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 $60.74   12.390%   $68.2657   $68.27   $68.25   $68.30  
  Purchase #2 $186.40   9.308%   $203.7501   $203.75   $203.75   $203.80  
  Purchase #3 $228.77   13.210%   $258.9905   $258.99   $259.00   $259.00  
  Purchase #4 $218.40   12.821%   $246.4011   $246.40   $246.40   $246.40  
  Purchase #5 $103.27   3.532%   $106.9175   $106.92   $106.90   $106.90  
  Purchase #6 $95.34   12.230%   $107.0001   $107.00   $107.00   $107.00  
  Purchase #7 $229.49   12.244%   $257.5888   $257.59   $257.60   $257.60  
  7 purchase totals = $1,122.41       $1,248.9138   $1,248.92   $1,248.90   $1,249.00