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 $47.46   13.489%   $53.8619   $53.86   $53.85   $53.90  
  Purchase #2 $13.72   6.349%   $14.5911   $14.59   $14.60   $14.60  
  Purchase #3 $246.32   10.256%   $271.5826   $271.58   $271.60   $271.60  
  Purchase #4 $249.88   3.707%   $259.1431   $259.14   $259.15   $259.10  
  Purchase #5 $63.81   4.762%   $66.8486   $66.85   $66.85   $66.80  
  Purchase #6 $243.97   5.678%   $257.8226   $257.82   $257.80   $257.80  
  Purchase #7 $186.65   3.638%   $193.4403   $193.44   $193.45   $193.40  
  7 purchase totals = $1,051.81       $1,117.2902   $1,117.28   $1,117.30   $1,117.20