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 $98.35   11.841%   $109.9956   $110.00   $110.00   $110.00  
  Purchase #2 $235.88   9.109%   $257.3663   $257.37   $257.35   $257.40  
  Purchase #3 $190.47   4.681%   $199.3859   $199.39   $199.40   $199.40  
  Purchase #4 $73.93   7.151%   $79.2167   $79.22   $79.20   $79.20  
  Purchase #5 $56.92   7.272%   $61.0592   $61.06   $61.05   $61.10  
  Purchase #6 $250.32   9.631%   $274.4283   $274.43   $274.45   $274.40  
  Purchase #7 $114.98   7.563%   $123.6759   $123.68   $123.70   $123.70  
  7 purchase totals = $1,020.85       $1,105.1279   $1,105.15   $1,105.15   $1,105.20