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 $246.81   10.576%   $272.9126   $272.91   $272.90   $272.90  
  Purchase #2 $213.31   10.640%   $236.0062   $236.01   $236.00   $236.00  
  Purchase #3 $62.45   3.355%   $64.5452   $64.55   $64.55   $64.50  
  Purchase #4 $218.34   6.644%   $232.8465   $232.85   $232.85   $232.80  
  Purchase #5 $183.77   6.239%   $195.2354   $195.24   $195.25   $195.20  
  Purchase #6 $5.59   10.197%   $6.16   $6.16   $6.15   $6.20  
  Purchase #7 $65.26   3.306%   $67.4175   $67.42   $67.40   $67.40  
  7 purchase totals = $995.53       $1,075.1234   $1,075.14   $1,075.10   $1,075.00