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 $72.78   12.693%   $82.018   $82.02   $82.00   $82.00  
  Purchase #2 $250.71   4.759%   $262.6413   $262.64   $262.65   $262.60  
  Purchase #3 $211.32   12.616%   $237.9801   $237.98   $238.00   $238.00  
  Purchase #4 $145.44   4.726%   $152.3135   $152.31   $152.30   $152.30  
  Purchase #5 $154.55   8.156%   $167.1551   $167.16   $167.15   $167.20  
  Purchase #6 $25.93   3.618%   $26.8681   $26.87   $26.85   $26.90  
  Purchase #7 $222.61   5.499%   $234.8513   $234.85   $234.85   $234.90  
  7 purchase totals = $1,083.34       $1,163.8274   $1,163.83   $1,163.80   $1,163.90