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 $214.44   4.450%   $223.9826   $223.98   $224.00   $224.00  
  Purchase #2 $201.79   8.632%   $219.2085   $219.21   $219.20   $219.20  
  Purchase #3 $227.94   3.393%   $235.674   $235.67   $235.65   $235.70  
  Purchase #4 $69.46   12.789%   $78.3432   $78.34   $78.35   $78.30  
  Purchase #5 $26.39   8.131%   $28.5358   $28.54   $28.55   $28.50  
  Purchase #6 $113.92   13.646%   $129.4655   $129.47   $129.45   $129.50  
  Purchase #7 $117.47   13.662%   $133.5188   $133.52   $133.50   $133.50  
  7 purchase totals = $971.41       $1,048.7284   $1,048.73   $1,048.70   $1,048.70