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 $248.82   4.111%   $259.049   $259.05   $259.05   $259.00  
  Purchase #2 $154.39   10.115%   $170.0065   $170.01   $170.00   $170.00  
  Purchase #3 $144.50   5.644%   $152.6556   $152.66   $152.65   $152.70  
  Purchase #4 $56.32   10.188%   $62.0579   $62.06   $62.05   $62.10  
  Purchase #5 $155.95   11.375%   $173.6893   $173.69   $173.70   $173.70  
  Purchase #6 $192.37   4.695%   $201.4018   $201.40   $201.40   $201.40  
  Purchase #7 $110.80   5.183%   $116.5428   $116.54   $116.55   $116.50  
  7 purchase totals = $1,063.15       $1,135.4029   $1,135.41   $1,135.40   $1,135.40