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 $202.59   7.766%   $218.3231   $218.32   $218.30   $218.30  
  Purchase #2 $8.28   9.433%   $9.0611   $9.06   $9.05   $9.10  
  Purchase #3 $78.63   4.416%   $82.1023   $82.10   $82.10   $82.10  
  Purchase #4 $59.30   6.224%   $62.9908   $62.99   $63.00   $63.00  
  Purchase #5 $249.43   3.611%   $258.4369   $258.44   $258.45   $258.40  
  Purchase #6 $156.75   9.332%   $171.3779   $171.38   $171.40   $171.40  
  Purchase #7 $194.33   3.521%   $201.1724   $201.17   $201.15   $201.20  
  7 purchase totals = $949.31       $1,003.4645   $1,003.46   $1,003.45   $1,003.50