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 $24.41   8.156%   $26.4009   $26.40   $26.40   $26.40  
  Purchase #2 $217.42   5.423%   $229.2107   $229.21   $229.20   $229.20  
  Purchase #3 $148.29   12.179%   $166.3502   $166.35   $166.35   $166.40  
  Purchase #4 $23.52   9.380%   $25.7262   $25.73   $25.75   $25.70  
  Purchase #5 $207.61   13.834%   $236.3308   $236.33   $236.35   $236.30  
  Purchase #6 $165.79   13.751%   $188.5878   $188.59   $188.60   $188.60  
  Purchase #7 $173.28   7.477%   $186.2361   $186.24   $186.25   $186.20  
  7 purchase totals = $960.32       $1,058.8427   $1,058.85   $1,058.90   $1,058.80