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 $219.85   10.244%   $242.3714   $242.37   $242.35   $242.40  
  Purchase #2 $120.87   12.219%   $135.6391   $135.64   $135.65   $135.60  
  Purchase #3 $221.57   7.185%   $237.4898   $237.49   $237.50   $237.50  
  Purchase #4 $168.48   3.551%   $174.4627   $174.46   $174.45   $174.50  
  Purchase #5 $24.92   13.298%   $28.2339   $28.23   $28.25   $28.20  
  Purchase #6 $22.76   3.622%   $23.5844   $23.58   $23.60   $23.60  
  Purchase #7 $219.64   7.172%   $235.3926   $235.39   $235.40   $235.40  
  7 purchase totals = $998.09       $1,077.1739   $1,077.16   $1,077.20   $1,077.20