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 $241.57   8.229%   $261.4488   $261.45   $261.45   $261.40  
  Purchase #2 $183.85   10.145%   $202.5016   $202.50   $202.50   $202.50  
  Purchase #3 $105.34   8.233%   $114.0126   $114.01   $114.00   $114.00  
  Purchase #4 $196.47   10.392%   $216.8872   $216.89   $216.90   $216.90  
  Purchase #5 $155.26   11.859%   $173.6723   $173.67   $173.65   $173.70  
  Purchase #6 $81.57   12.413%   $91.6953   $91.70   $91.70   $91.70  
  Purchase #7 $126.55   9.364%   $138.4001   $138.40   $138.40   $138.40  
  7 purchase totals = $1,090.61       $1,198.6179   $1,198.62   $1,198.60   $1,198.60