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 $246.87   8.416%   $267.6466   $267.65   $267.65   $267.60  
  Purchase #2 $5.54   4.252%   $5.7756   $5.78   $5.80   $5.80  
  Purchase #3 $33.87   6.779%   $36.166   $36.17   $36.15   $36.20  
  Purchase #4 $240.69   7.396%   $258.4914   $258.49   $258.50   $258.50  
  Purchase #5 $228.93   12.607%   $257.7912   $257.79   $257.80   $257.80  
  Purchase #6 $102.88   4.477%   $107.4859   $107.49   $107.50   $107.50  
  Purchase #7 $135.67   5.833%   $143.5836   $143.58   $143.60   $143.60  
  7 purchase totals = $994.45       $1,076.9403   $1,076.95   $1,077.00   $1,077.00