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 $250.94   10.190%   $276.5108   $276.51   $276.50   $276.50  
  Purchase #2 $75.71   5.845%   $80.1352   $80.14   $80.15   $80.10  
  Purchase #3 $96.46   11.589%   $107.6387   $107.64   $107.65   $107.60  
  Purchase #4 $155.53   6.668%   $165.9007   $165.90   $165.90   $165.90  
  Purchase #5 $114.36   5.260%   $120.3753   $120.38   $120.40   $120.40  
  Purchase #6 $208.80   13.809%   $237.6332   $237.63   $237.65   $237.60  
  Purchase #7 $16.89   11.380%   $18.8121   $18.81   $18.80   $18.80  
  7 purchase totals = $918.69       $1,007.0060   $1,007.01   $1,007.05   $1,006.90