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 $241.46   6.756%   $257.773   $257.77   $257.75   $257.80  
  Purchase #2 $137.88   4.477%   $144.0529   $144.05   $144.05   $144.10  
  Purchase #3 $42.48   3.537%   $43.9825   $43.98   $44.00   $44.00  
  Purchase #4 $138.76   12.495%   $156.0981   $156.10   $156.10   $156.10  
  Purchase #5 $160.27   11.723%   $179.0585   $179.06   $179.05   $179.10  
  Purchase #6 $88.67   8.787%   $96.4614   $96.46   $96.45   $96.50  
  Purchase #7 $44.89   3.674%   $46.5393   $46.54   $46.55   $46.50  
  7 purchase totals = $854.41       $923.9657   $923.96   $923.95   $924.10