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 $24.76   4.611%   $25.9017   $25.90   $25.90   $25.90  
  Purchase #2 $212.69   5.199%   $223.7478   $223.75   $223.75   $223.70  
  Purchase #3 $208.69   13.407%   $236.6691   $236.67   $236.65   $236.70  
  Purchase #4 $57.57   3.225%   $59.4266   $59.43   $59.45   $59.40  
  Purchase #5 $179.32   3.187%   $185.0349   $185.03   $185.05   $185.00  
  Purchase #6 $131.57   12.262%   $147.7031   $147.70   $147.70   $147.70  
  Purchase #7 $161.54   11.569%   $180.2286   $180.23   $180.25   $180.20  
  7 purchase totals = $976.14       $1,058.7118   $1,058.71   $1,058.75   $1,058.60