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 $46.62   6.281%   $49.5482   $49.55   $49.55   $49.50  
  Purchase #2 $215.64   10.711%   $238.7372   $238.74   $238.75   $238.70  
  Purchase #3 $240.37   8.635%   $261.1259   $261.13   $261.15   $261.10  
  Purchase #4 $106.67   6.675%   $113.7902   $113.79   $113.80   $113.80  
  Purchase #5 $81.40   3.387%   $84.157   $84.16   $84.15   $84.20  
  Purchase #6 $218.60   5.744%   $231.1564   $231.16   $231.15   $231.20  
  Purchase #7 $31.35   10.284%   $34.574   $34.57   $34.55   $34.60  
  7 purchase totals = $940.65       $1,013.0889   $1,013.10   $1,013.10   $1,013.10