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 $152.55   8.206%   $165.0683   $165.07   $165.05   $165.10  
  Purchase #2 $105.48   7.671%   $113.5714   $113.57   $113.55   $113.60  
  Purchase #3 $143.55   9.860%   $157.704   $157.70   $157.70   $157.70  
  Purchase #4 $36.60   12.671%   $41.2376   $41.24   $41.25   $41.20  
  Purchase #5 $236.69   9.441%   $259.0359   $259.04   $259.05   $259.00  
  Purchase #6 $26.99   7.441%   $28.9983   $29.00   $29.00   $29.00  
  Purchase #7 $59.43   3.369%   $61.4322   $61.43   $61.45   $61.40  
  7 purchase totals = $761.29       $827.0477   $827.05   $827.05   $827.00