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 $197.68   13.271%   $223.9141   $223.91   $223.90   $223.90  
  Purchase #2 $34.46   4.571%   $36.0352   $36.04   $36.05   $36.00  
  Purchase #3 $76.69   5.849%   $81.1756   $81.18   $81.20   $81.20  
  Purchase #4 $229.56   12.647%   $258.5925   $258.59   $258.60   $258.60  
  Purchase #5 $58.96   3.470%   $61.0059   $61.01   $61.00   $61.00  
  Purchase #6 $34.65   5.243%   $36.4667   $36.47   $36.45   $36.50  
  Purchase #7 $204.76   10.768%   $226.8086   $226.81   $226.80   $226.80  
  7 purchase totals = $836.76       $923.9986   $924.01   $924.00   $924.00