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 $211.46   5.841%   $223.8114   $223.81   $223.80   $223.80  
  Purchase #2 $77.42   8.815%   $84.2446   $84.24   $84.25   $84.20  
  Purchase #3 $91.67   7.767%   $98.79   $98.79   $98.80   $98.80  
  Purchase #4 $182.51   3.268%   $188.4744   $188.47   $188.45   $188.50  
  Purchase #5 $229.44   9.110%   $250.342   $250.34   $250.35   $250.30  
  Purchase #6 $98.54   11.185%   $109.5617   $109.56   $109.55   $109.60  
  Purchase #7 $48.86   3.239%   $50.4426   $50.44   $50.45   $50.40  
  7 purchase totals = $939.90       $1,005.6667   $1,005.65   $1,005.65   $1,005.60