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 $116.76   13.717%   $132.776   $132.78   $132.80   $132.80  
  Purchase #2 $26.61   9.187%   $29.0547   $29.05   $29.05   $29.10  
  Purchase #3 $208.87   10.487%   $230.7742   $230.77   $230.75   $230.80  
  Purchase #4 $209.86   8.717%   $228.1535   $228.15   $228.15   $228.20  
  Purchase #5 $106.83   4.788%   $111.945   $111.95   $111.95   $111.90  
  Purchase #6 $236.45   9.102%   $257.9717   $257.97   $257.95   $258.00  
  Purchase #7 $49.51   9.113%   $54.0218   $54.02   $54.00   $54.00  
  7 purchase totals = $954.89       $1,044.6969   $1,044.69   $1,044.65   $1,044.80