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 $232.37   10.787%   $257.4358   $257.44   $257.45   $257.40  
  Purchase #2 $116.85   11.556%   $130.3532   $130.35   $130.35   $130.40  
  Purchase #3 $24.48   10.866%   $27.14   $27.14   $27.15   $27.10  
  Purchase #4 $117.91   6.194%   $125.2133   $125.21   $125.20   $125.20  
  Purchase #5 $93.68   7.328%   $100.5449   $100.54   $100.55   $100.50  
  Purchase #6 $221.25   9.137%   $241.4656   $241.47   $241.45   $241.50  
  Purchase #7 $144.50   6.330%   $153.6469   $153.65   $153.65   $153.60  
  7 purchase totals = $951.04       $1,035.7997   $1,035.80   $1,035.80   $1,035.70