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 $196.99   5.552%   $207.9269   $207.93   $207.95   $207.90  
  Purchase #2 $120.55   3.740%   $125.0586   $125.06   $125.05   $125.10  
  Purchase #3 $96.53   3.253%   $99.6701   $99.67   $99.65   $99.70  
  Purchase #4 $127.25   6.568%   $135.6078   $135.61   $135.60   $135.60  
  Purchase #5 $66.90   11.714%   $74.7367   $74.74   $74.75   $74.70  
  Purchase #6 $234.40   10.373%   $258.7143   $258.71   $258.70   $258.70  
  Purchase #7 $116.87   5.387%   $123.1658   $123.17   $123.15   $123.20  
  7 purchase totals = $959.49       $1,024.8802   $1,024.89   $1,024.85   $1,024.90