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 $190.54   8.771%   $207.2523   $207.25   $207.25   $207.30  
  Purchase #2 $187.41   8.409%   $203.1693   $203.17   $203.15   $203.20  
  Purchase #3 $83.69   9.665%   $91.7786   $91.78   $91.80   $91.80  
  Purchase #4 $249.89   9.555%   $273.767   $273.77   $273.75   $273.80  
  Purchase #5 $35.65   6.544%   $37.9829   $37.98   $38.00   $38.00  
  Purchase #6 $74.80   5.767%   $79.1137   $79.11   $79.10   $79.10  
  Purchase #7 $138.33   3.427%   $143.0706   $143.07   $143.05   $143.10  
  7 purchase totals = $960.31       $1,036.1344   $1,036.13   $1,036.10   $1,036.30