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 $168.58   7.719%   $181.5927   $181.59   $181.60   $181.60  
  Purchase #2 $235.61   12.252%   $264.4769   $264.48   $264.50   $264.50  
  Purchase #3 $157.26   6.497%   $167.4772   $167.48   $167.50   $167.50  
  Purchase #4 $47.41   13.764%   $53.9355   $53.94   $53.95   $53.90  
  Purchase #5 $182.80   10.398%   $201.8075   $201.81   $201.80   $201.80  
  Purchase #6 $70.31   8.570%   $76.3356   $76.34   $76.35   $76.30  
  Purchase #7 $87.85   8.668%   $95.4648   $95.46   $95.45   $95.50  
  7 purchase totals = $949.82       $1,041.0902   $1,041.10   $1,041.15   $1,041.10