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 $47.36   7.388%   $50.859   $50.86   $50.85   $50.90  
  Purchase #2 $214.58   13.516%   $243.5826   $243.58   $243.60   $243.60  
  Purchase #3 $23.47   3.562%   $24.306   $24.31   $24.30   $24.30  
  Purchase #4 $179.88   10.235%   $198.2907   $198.29   $198.30   $198.30  
  Purchase #5 $33.83   12.158%   $37.9431   $37.94   $37.95   $37.90  
  Purchase #6 $186.93   8.437%   $202.7013   $202.70   $202.70   $202.70  
  Purchase #7 $127.83   3.253%   $131.9883   $131.99   $132.00   $132.00  
  7 purchase totals = $813.88       $889.6710   $889.67   $889.70   $889.70