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 $35.98   11.714%   $40.1947   $40.19   $40.20   $40.20  
  Purchase #2 $221.47   5.724%   $234.1469   $234.15   $234.15   $234.10  
  Purchase #3 $80.27   9.817%   $88.1501   $88.15   $88.15   $88.20  
  Purchase #4 $164.86   8.693%   $179.1913   $179.19   $179.20   $179.20  
  Purchase #5 $127.44   8.608%   $138.41   $138.41   $138.40   $138.40  
  Purchase #6 $225.30   13.858%   $256.5221   $256.52   $256.50   $256.50  
  Purchase #7 $102.25   5.465%   $107.838   $107.84   $107.85   $107.80  
  7 purchase totals = $957.57       $1,044.4531   $1,044.45   $1,044.45   $1,044.40