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 $163.34   8.593%   $177.3758   $177.38   $177.40   $177.40  
  Purchase #2 $86.32   7.639%   $92.914   $92.91   $92.90   $92.90  
  Purchase #3 $12.61   13.155%   $14.2688   $14.27   $14.25   $14.30  
  Purchase #4 $131.96   13.591%   $149.8947   $149.89   $149.90   $149.90  
  Purchase #5 $161.91   3.569%   $167.6886   $167.69   $167.70   $167.70  
  Purchase #6 $154.94   6.721%   $165.3535   $165.35   $165.35   $165.40  
  Purchase #7 $217.76   5.791%   $230.3705   $230.37   $230.35   $230.40  
  7 purchase totals = $928.84       $997.8659   $997.86   $997.85   $998.00