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 $95.69   6.115%   $101.5414   $101.54   $101.55   $101.50  
  Purchase #2 $44.39   7.753%   $47.8316   $47.83   $47.85   $47.80  
  Purchase #3 $240.35   6.542%   $256.0737   $256.07   $256.05   $256.10  
  Purchase #4 $38.25   10.145%   $42.1305   $42.13   $42.15   $42.10  
  Purchase #5 $100.26   6.537%   $106.814   $106.81   $106.80   $106.80  
  Purchase #6 $201.70   13.292%   $228.51   $228.51   $228.50   $228.50  
  Purchase #7 $222.40   8.485%   $241.2706   $241.27   $241.25   $241.30  
  7 purchase totals = $943.04       $1,024.1718   $1,024.16   $1,024.15   $1,024.10