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 $63.99   8.874%   $69.6685   $69.67   $69.65   $69.70  
  Purchase #2 $131.25   5.560%   $138.5475   $138.55   $138.55   $138.50  
  Purchase #3 $158.64   10.592%   $175.4431   $175.44   $175.45   $175.40  
  Purchase #4 $250.69   3.207%   $258.7296   $258.73   $258.75   $258.70  
  Purchase #5 $33.52   5.423%   $35.3378   $35.34   $35.35   $35.30  
  Purchase #6 $144.67   6.616%   $154.2414   $154.24   $154.25   $154.20  
  Purchase #7 $174.82   8.478%   $189.6412   $189.64   $189.65   $189.60  
  7 purchase totals = $957.58       $1,021.6091   $1,021.61   $1,021.65   $1,021.40