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 $222.66   12.395%   $250.2587   $250.26   $250.25   $250.30  
  Purchase #2 $70.90   6.644%   $75.6106   $75.61   $75.60   $75.60  
  Purchase #3 $122.37   3.334%   $126.4498   $126.45   $126.45   $126.40  
  Purchase #4 $79.51   5.174%   $83.6238   $83.62   $83.60   $83.60  
  Purchase #5 $86.56   10.254%   $95.4359   $95.44   $95.45   $95.40  
  Purchase #6 $181.56   13.605%   $206.2612   $206.26   $206.25   $206.30  
  Purchase #7 $202.28   6.278%   $214.9791   $214.98   $215.00   $215.00  
  7 purchase totals = $965.84       $1,052.6191   $1,052.62   $1,052.60   $1,052.60