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 $60.48   6.332%   $64.3096   $64.31   $64.30   $64.30  
  Purchase #2 $152.36   7.379%   $163.6026   $163.60   $163.60   $163.60  
  Purchase #3 $169.92   7.169%   $182.1016   $182.10   $182.10   $182.10  
  Purchase #4 $171.73   3.352%   $177.4864   $177.49   $177.50   $177.50  
  Purchase #5 $236.87   3.474%   $245.0989   $245.10   $245.10   $245.10  
  Purchase #6 $77.35   8.174%   $83.6726   $83.67   $83.65   $83.70  
  Purchase #7 $80.86   6.836%   $86.3876   $86.39   $86.40   $86.40  
  7 purchase totals = $949.57       $1,002.6593   $1,002.66   $1,002.65   $1,002.70