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 $60.55   11.619%   $67.5853   $67.59   $67.60   $67.60  
  Purchase #2 $147.26   6.404%   $156.6905   $156.69   $156.70   $156.70  
  Purchase #3 $119.45   4.175%   $124.437   $124.44   $124.45   $124.40  
  Purchase #4 $173.71   3.412%   $179.637   $179.64   $179.65   $179.60  
  Purchase #5 $60.80   10.533%   $67.2041   $67.20   $67.20   $67.20  
  Purchase #6 $128.62   4.850%   $134.8581   $134.86   $134.85   $134.90  
  Purchase #7 $230.33   7.764%   $248.2128   $248.21   $248.20   $248.20  
  7 purchase totals = $920.72       $978.6248   $978.63   $978.65   $978.60