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 $57.26   10.637%   $63.3507   $63.35   $63.35   $63.40  
  Purchase #2 $208.80   9.759%   $229.1768   $229.18   $229.20   $229.20  
  Purchase #3 $171.36   12.839%   $193.3609   $193.36   $193.35   $193.40  
  Purchase #4 $88.45   6.569%   $94.2603   $94.26   $94.25   $94.30  
  Purchase #5 $108.85   7.818%   $117.3599   $117.36   $117.35   $117.40  
  Purchase #6 $208.34   11.193%   $231.6595   $231.66   $231.65   $231.70  
  Purchase #7 $50.76   5.533%   $53.5686   $53.57   $53.55   $53.60  
  7 purchase totals = $893.82       $982.7367   $982.74   $982.70   $983.00