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 $161.86   7.276%   $173.6369   $173.64   $173.65   $173.60  
  Purchase #2 $67.80   8.124%   $73.3081   $73.31   $73.30   $73.30  
  Purchase #3 $118.65   12.695%   $133.7126   $133.71   $133.70   $133.70  
  Purchase #4 $223.96   11.760%   $250.2977   $250.30   $250.30   $250.30  
  Purchase #5 $164.83   6.520%   $175.5769   $175.58   $175.60   $175.60  
  Purchase #6 $176.51   11.381%   $196.5986   $196.60   $196.60   $196.60  
  Purchase #7 $93.92   11.580%   $104.7959   $104.80   $104.80   $104.80  
  7 purchase totals = $1,007.53       $1,107.9267   $1,107.94   $1,107.95   $1,107.90