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 $28.36   12.387%   $31.873   $31.87   $31.85   $31.90  
  Purchase #2 $54.48   9.449%   $59.6278   $59.63   $59.65   $59.60  
  Purchase #3 $60.41   12.299%   $67.8398   $67.84   $67.85   $67.80  
  Purchase #4 $137.57   11.110%   $152.854   $152.85   $152.85   $152.90  
  Purchase #5 $199.76   10.779%   $221.2921   $221.29   $221.30   $221.30  
  Purchase #6 $163.70   8.272%   $177.2413   $177.24   $177.25   $177.20  
  Purchase #7 $225.57   6.342%   $239.8756   $239.88   $239.90   $239.90  
  7 purchase totals = $869.85       $950.6036   $950.60   $950.65   $950.60