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 $248.28   5.431%   $261.7641   $261.76   $261.75   $261.80  
  Purchase #2 $49.89   5.708%   $52.7377   $52.74   $52.75   $52.70  
  Purchase #3 $228.55   9.873%   $251.1147   $251.11   $251.10   $251.10  
  Purchase #4 $99.62   7.174%   $106.7667   $106.77   $106.75   $106.80  
  Purchase #5 $213.53   5.658%   $225.6115   $225.61   $225.60   $225.60  
  Purchase #6 $155.26   6.602%   $165.5103   $165.51   $165.50   $165.50  
  Purchase #7 $59.90   9.767%   $65.7504   $65.75   $65.75   $65.80  
  7 purchase totals = $1,055.03       $1,129.2554   $1,129.25   $1,129.20   $1,129.30