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 $176.41   4.136%   $183.7063   $183.71   $183.70   $183.70  
  Purchase #2 $221.80   11.295%   $246.8523   $246.85   $246.85   $246.90  
  Purchase #3 $98.90   13.340%   $112.0933   $112.09   $112.10   $112.10  
  Purchase #4 $241.49   6.449%   $257.0637   $257.06   $257.05   $257.10  
  Purchase #5 $138.93   8.154%   $150.2584   $150.26   $150.25   $150.30  
  Purchase #6 $101.54   3.197%   $104.7862   $104.79   $104.80   $104.80  
  Purchase #7 $26.25   11.143%   $29.175   $29.18   $29.20   $29.20  
  7 purchase totals = $1,005.32       $1,083.9352   $1,083.94   $1,083.95   $1,084.10