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 $57.64   13.529%   $65.4381   $65.44   $65.45   $65.40  
  Purchase #2 $181.87   6.633%   $193.9334   $193.93   $193.95   $193.90  
  Purchase #3 $240.56   7.543%   $258.7054   $258.71   $258.70   $258.70  
  Purchase #4 $212.76   13.671%   $241.8464   $241.85   $241.85   $241.80  
  Purchase #5 $215.29   10.858%   $238.6662   $238.67   $238.65   $238.70  
  Purchase #6 $100.33   7.216%   $107.5698   $107.57   $107.55   $107.60  
  Purchase #7 $173.93   13.227%   $196.9357   $196.94   $196.95   $196.90  
  7 purchase totals = $1,182.38       $1,303.0950   $1,303.11   $1,303.10   $1,303.00