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 $106.56   6.577%   $113.5685   $113.57   $113.55   $113.60  
  Purchase #2 $134.63   13.357%   $152.6125   $152.61   $152.60   $152.60  
  Purchase #3 $125.75   4.695%   $131.654   $131.65   $131.65   $131.70  
  Purchase #4 $161.26   3.692%   $167.2137   $167.21   $167.20   $167.20  
  Purchase #5 $226.69   11.349%   $252.417   $252.42   $252.40   $252.40  
  Purchase #6 $17.54   6.257%   $18.6375   $18.64   $18.65   $18.60  
  Purchase #7 $120.94   8.687%   $131.4461   $131.45   $131.45   $131.40  
  7 purchase totals = $893.37       $967.5493   $967.55   $967.50   $967.50