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 $172.61   13.568%   $196.0297   $196.03   $196.05   $196.00  
  Purchase #2 $24.48   9.610%   $26.8325   $26.83   $26.85   $26.80  
  Purchase #3 $178.59   8.314%   $193.438   $193.44   $193.45   $193.40  
  Purchase #4 $153.67   8.828%   $167.236   $167.24   $167.25   $167.20  
  Purchase #5 $24.84   8.314%   $26.9052   $26.91   $26.90   $26.90  
  Purchase #6 $193.65   5.452%   $204.2078   $204.21   $204.20   $204.20  
  Purchase #7 $67.69   12.265%   $75.9922   $75.99   $76.00   $76.00  
  7 purchase totals = $815.53       $890.6414   $890.65   $890.70   $890.50