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 $162.30   10.506%   $179.3512   $179.35   $179.35   $179.40  
  Purchase #2 $136.26   8.581%   $147.9525   $147.95   $147.95   $148.00  
  Purchase #3 $169.91   10.785%   $188.2348   $188.23   $188.25   $188.20  
  Purchase #4 $29.26   4.434%   $30.5574   $30.56   $30.55   $30.60  
  Purchase #5 $209.94   13.569%   $238.4268   $238.43   $238.45   $238.40  
  Purchase #6 $91.39   3.682%   $94.755   $94.76   $94.75   $94.80  
  Purchase #7 $125.66   7.357%   $134.9048   $134.90   $134.90   $134.90  
  7 purchase totals = $924.72       $1,014.1825   $1,014.18   $1,014.20   $1,014.30