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 $16.87   5.684%   $17.8289   $17.83   $17.85   $17.80  
  Purchase #2 $120.66   12.648%   $135.9211   $135.92   $135.90   $135.90  
  Purchase #3 $75.62   3.233%   $78.0648   $78.06   $78.05   $78.10  
  Purchase #4 $110.30   4.317%   $115.0617   $115.06   $115.05   $115.10  
  Purchase #5 $113.55   5.126%   $119.3706   $119.37   $119.35   $119.40  
  Purchase #6 $99.87   7.419%   $107.2794   $107.28   $107.30   $107.30  
  Purchase #7 $72.30   10.705%   $80.0397   $80.04   $80.05   $80.00  
  7 purchase totals = $609.17       $653.5662   $653.56   $653.55   $653.60