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 $85.58   12.208%   $96.0276   $96.03   $96.05   $96.00  
  Purchase #2 $57.77   3.712%   $59.9144   $59.91   $59.90   $59.90  
  Purchase #3 $202.85   5.217%   $213.4327   $213.43   $213.45   $213.40  
  Purchase #4 $219.41   13.504%   $249.0391   $249.04   $249.05   $249.00  
  Purchase #5 $133.56   10.302%   $147.3194   $147.32   $147.30   $147.30  
  Purchase #6 $247.80   5.432%   $261.2605   $261.26   $261.25   $261.30  
  Purchase #7 $47.59   3.587%   $49.2971   $49.30   $49.30   $49.30  
  7 purchase totals = $994.56       $1,076.2908   $1,076.29   $1,076.30   $1,076.20