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 $203.61   4.155%   $212.07   $212.07   $212.05   $212.10  
  Purchase #2 $201.31   3.149%   $207.6493   $207.65   $207.65   $207.60  
  Purchase #3 $30.83   8.595%   $33.4798   $33.48   $33.50   $33.50  
  Purchase #4 $131.40   6.684%   $140.1828   $140.18   $140.20   $140.20  
  Purchase #5 $80.55   3.353%   $83.2508   $83.25   $83.25   $83.30  
  Purchase #6 $73.42   6.426%   $78.138   $78.14   $78.15   $78.10  
  Purchase #7 $230.26   10.463%   $254.3521   $254.35   $254.35   $254.40  
  7 purchase totals = $951.38       $1,009.1228   $1,009.12   $1,009.15   $1,009.20