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 $64.46   13.319%   $73.0454   $73.05   $73.05   $73.00  
  Purchase #2 $226.42   10.476%   $250.1398   $250.14   $250.15   $250.10  
  Purchase #3 $23.87   4.661%   $24.9826   $24.98   $25.00   $25.00  
  Purchase #4 $11.84   4.747%   $12.402   $12.40   $12.40   $12.40  
  Purchase #5 $152.96   3.866%   $158.8734   $158.87   $158.85   $158.90  
  Purchase #6 $163.35   11.223%   $181.6828   $181.68   $181.70   $181.70  
  Purchase #7 $243.69   7.523%   $262.0228   $262.02   $262.00   $262.00  
  7 purchase totals = $886.59       $963.1488   $963.14   $963.15   $963.10