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 $175.65   6.460%   $186.997   $187.00   $187.00   $187.00  
  Purchase #2 $245.33   4.134%   $255.4719   $255.47   $255.45   $255.50  
  Purchase #3 $132.50   6.414%   $140.9986   $141.00   $141.00   $141.00  
  Purchase #4 $66.44   9.255%   $72.589   $72.59   $72.60   $72.60  
  Purchase #5 $192.72   7.755%   $207.6654   $207.67   $207.65   $207.70  
  Purchase #6 $211.35   11.268%   $235.1649   $235.16   $235.15   $235.20  
  Purchase #7 $27.50   11.724%   $30.7241   $30.72   $30.70   $30.70  
  7 purchase totals = $1,051.49       $1,129.6109   $1,129.61   $1,129.55   $1,129.70