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 $63.53   8.718%   $69.0685   $69.07   $69.05   $69.10  
  Purchase #2 $151.36   9.361%   $165.5288   $165.53   $165.55   $165.50  
  Purchase #3 $59.39   6.200%   $63.0722   $63.07   $63.05   $63.10  
  Purchase #4 $233.40   13.765%   $265.5275   $265.53   $265.55   $265.50  
  Purchase #5 $220.28   13.731%   $250.5266   $250.53   $250.55   $250.50  
  Purchase #6 $136.46   9.350%   $149.219   $149.22   $149.20   $149.20  
  Purchase #7 $5.65   7.705%   $6.0853   $6.09   $6.10   $6.10  
  7 purchase totals = $870.07       $969.0279   $969.04   $969.05   $969.00