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 $204.88   3.507%   $212.0651   $212.07   $212.05   $212.10  
  Purchase #2 $107.30   9.386%   $117.3712   $117.37   $117.35   $117.40  
  Purchase #3 $243.83   9.663%   $267.3913   $267.39   $267.40   $267.40  
  Purchase #4 $53.58   5.660%   $56.6126   $56.61   $56.60   $56.60  
  Purchase #5 $35.43   7.712%   $38.1624   $38.16   $38.15   $38.20  
  Purchase #6 $122.64   9.430%   $134.205   $134.21   $134.20   $134.20  
  Purchase #7 $173.50   5.229%   $182.5723   $182.57   $182.55   $182.60  
  7 purchase totals = $941.16       $1,008.3799   $1,008.38   $1,008.30   $1,008.50