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 $148.86   10.264%   $164.139   $164.14   $164.15   $164.10  
  Purchase #2 $155.66   12.433%   $175.0132   $175.01   $175.00   $175.00  
  Purchase #3 $152.46   6.630%   $162.5681   $162.57   $162.55   $162.60  
  Purchase #4 $45.54   4.189%   $47.4477   $47.45   $47.45   $47.40  
  Purchase #5 $238.94   6.289%   $253.9669   $253.97   $253.95   $254.00  
  Purchase #6 $122.73   11.840%   $137.2612   $137.26   $137.25   $137.30  
  Purchase #7 $128.25   5.323%   $135.0767   $135.08   $135.10   $135.10  
  7 purchase totals = $992.44       $1,075.4728   $1,075.48   $1,075.45   $1,075.50