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 $126.93   10.860%   $140.7146   $140.71   $140.70   $140.70  
  Purchase #2 $205.75   9.871%   $226.0596   $226.06   $226.05   $226.10  
  Purchase #3 $58.49   10.794%   $64.8034   $64.80   $64.80   $64.80  
  Purchase #4 $172.35   12.251%   $193.4646   $193.46   $193.45   $193.50  
  Purchase #5 $179.84   10.188%   $198.1621   $198.16   $198.15   $198.20  
  Purchase #6 $131.49   10.151%   $144.8375   $144.84   $144.85   $144.80  
  Purchase #7 $100.70   13.759%   $114.5553   $114.56   $114.55   $114.60  
  7 purchase totals = $975.55       $1,082.5971   $1,082.59   $1,082.55   $1,082.70