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 $24.55   3.185%   $25.3319   $25.33   $25.35   $25.30  
  Purchase #2 $181.25   13.860%   $206.3713   $206.37   $206.35   $206.40  
  Purchase #3 $179.41   6.856%   $191.7103   $191.71   $191.70   $191.70  
  Purchase #4 $41.93   7.562%   $45.1007   $45.10   $45.10   $45.10  
  Purchase #5 $65.50   6.741%   $69.9154   $69.92   $69.90   $69.90  
  Purchase #6 $174.87   6.724%   $186.6283   $186.63   $186.65   $186.60  
  Purchase #7 $31.88   4.462%   $33.3025   $33.30   $33.30   $33.30  
  7 purchase totals = $699.39       $758.3604   $758.36   $758.35   $758.30