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 $233.55   3.170%   $240.9535   $240.95   $240.95   $241.00  
  Purchase #2 $130.91   9.257%   $143.0283   $143.03   $143.05   $143.00  
  Purchase #3 $24.94   10.423%   $27.5395   $27.54   $27.55   $27.50  
  Purchase #4 $242.57   3.458%   $250.9581   $250.96   $250.95   $251.00  
  Purchase #5 $211.98   5.141%   $222.8779   $222.88   $222.90   $222.90  
  Purchase #6 $216.56   11.473%   $241.4059   $241.41   $241.40   $241.40  
  Purchase #7 $95.65   6.323%   $101.6979   $101.70   $101.70   $101.70  
  7 purchase totals = $1,156.16       $1,228.4611   $1,228.47   $1,228.50   $1,228.50