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 $145.89   10.285%   $160.8948   $160.89   $160.90   $160.90  
  Purchase #2 $12.25   13.245%   $13.8725   $13.87   $13.85   $13.90  
  Purchase #3 $198.54   4.305%   $207.0871   $207.09   $207.10   $207.10  
  Purchase #4 $28.54   6.582%   $30.4185   $30.42   $30.40   $30.40  
  Purchase #5 $66.37   6.223%   $70.5002   $70.50   $70.50   $70.50  
  Purchase #6 $141.49   7.814%   $152.546   $152.55   $152.55   $152.50  
  Purchase #7 $150.43   9.284%   $164.3959   $164.40   $164.40   $164.40  
  7 purchase totals = $743.51       $799.7150   $799.72   $799.70   $799.70