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 $241.40   9.486%   $264.2992   $264.30   $264.30   $264.30  
  Purchase #2 $112.90   9.561%   $123.6944   $123.69   $123.70   $123.70  
  Purchase #3 $228.40   8.332%   $247.4303   $247.43   $247.45   $247.40  
  Purchase #4 $26.49   7.620%   $28.5085   $28.51   $28.50   $28.50  
  Purchase #5 $70.66   13.775%   $80.3934   $80.39   $80.40   $80.40  
  Purchase #6 $163.43   7.738%   $176.0762   $176.08   $176.10   $176.10  
  Purchase #7 $119.30   5.648%   $126.0381   $126.04   $126.05   $126.00  
  7 purchase totals = $962.58       $1,046.4401   $1,046.44   $1,046.50   $1,046.40