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 $241.68   8.259%   $261.6404   $261.64   $261.65   $261.60  
  Purchase #2 $151.52   10.647%   $167.6523   $167.65   $167.65   $167.70  
  Purchase #3 $11.36   3.849%   $11.7972   $11.80   $11.80   $11.80  
  Purchase #4 $196.43   11.630%   $219.2748   $219.27   $219.25   $219.30  
  Purchase #5 $190.98   12.344%   $214.5546   $214.55   $214.55   $214.60  
  Purchase #6 $161.80   5.750%   $171.1035   $171.10   $171.10   $171.10  
  Purchase #7 $81.30   12.623%   $91.5625   $91.56   $91.55   $91.60  
  7 purchase totals = $1,035.07       $1,137.5853   $1,137.57   $1,137.55   $1,137.70