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 $190.95   5.653%   $201.7444   $201.74   $201.75   $201.70  
  Purchase #2 $70.37   6.335%   $74.8279   $74.83   $74.85   $74.80  
  Purchase #3 $151.89   5.396%   $160.086   $160.09   $160.10   $160.10  
  Purchase #4 $124.79   13.693%   $141.8775   $141.88   $141.90   $141.90  
  Purchase #5 $30.59   3.615%   $31.6958   $31.70   $31.70   $31.70  
  Purchase #6 $88.27   5.224%   $92.8812   $92.88   $92.90   $92.90  
  Purchase #7 $225.40   5.114%   $236.927   $236.93   $236.95   $236.90  
  7 purchase totals = $882.26       $940.0398   $940.05   $940.15   $940.00