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 $53.81   5.285%   $56.6539   $56.65   $56.65   $56.70  
  Purchase #2 $163.44   6.737%   $174.451   $174.45   $174.45   $174.50  
  Purchase #3 $118.49   12.746%   $133.5927   $133.59   $133.60   $133.60  
  Purchase #4 $217.79   12.848%   $245.7717   $245.77   $245.75   $245.80  
  Purchase #5 $122.28   8.798%   $133.0382   $133.04   $133.05   $133.00  
  Purchase #6 $219.35   8.744%   $238.53   $238.53   $238.55   $238.50  
  Purchase #7 $35.52   12.684%   $40.0254   $40.03   $40.05   $40.00  
  7 purchase totals = $930.68       $1,022.0629   $1,022.06   $1,022.10   $1,022.10