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 $121.51   10.764%   $134.5893   $134.59   $134.60   $134.60  
  Purchase #2 $215.36   6.244%   $228.8071   $228.81   $228.80   $228.80  
  Purchase #3 $190.72   8.323%   $206.5936   $206.59   $206.60   $206.60  
  Purchase #4 $198.78   6.475%   $211.651   $211.65   $211.65   $211.70  
  Purchase #5 $206.33   13.624%   $234.4404   $234.44   $234.45   $234.40  
  Purchase #6 $199.72   4.361%   $208.4298   $208.43   $208.45   $208.40  
  Purchase #7 $245.70   12.781%   $277.1029   $277.10   $277.10   $277.10  
  7 purchase totals = $1,378.12       $1,501.6141   $1,501.61   $1,501.65   $1,501.60