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 $242.53   8.200%   $262.4175   $262.42   $262.40   $262.40  
  Purchase #2 $133.42   10.693%   $147.6866   $147.69   $147.70   $147.70  
  Purchase #3 $74.47   12.651%   $83.8912   $83.89   $83.90   $83.90  
  Purchase #4 $193.94   8.209%   $209.8605   $209.86   $209.85   $209.90  
  Purchase #5 $11.66   4.190%   $12.1486   $12.15   $12.15   $12.10  
  Purchase #6 $125.51   4.818%   $131.5571   $131.56   $131.55   $131.60  
  Purchase #7 $204.33   8.637%   $221.978   $221.98   $222.00   $222.00  
  7 purchase totals = $985.86       $1,069.5395   $1,069.55   $1,069.55   $1,069.60