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 $201.34   3.281%   $207.946   $207.95   $207.95   $207.90  
  Purchase #2 $212.60   9.390%   $232.5631   $232.56   $232.55   $232.60  
  Purchase #3 $20.72   8.648%   $22.5119   $22.51   $22.50   $22.50  
  Purchase #4 $130.57   12.205%   $146.5061   $146.51   $146.50   $146.50  
  Purchase #5 $74.44   10.702%   $82.4066   $82.41   $82.40   $82.40  
  Purchase #6 $177.95   13.867%   $202.6263   $202.63   $202.65   $202.60  
  Purchase #7 $227.31   6.851%   $242.883   $242.88   $242.90   $242.90  
  7 purchase totals = $1,044.93       $1,137.4430   $1,137.45   $1,137.45   $1,137.40