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 $44.81   12.768%   $50.5313   $50.53   $50.55   $50.50  
  Purchase #2 $219.69   12.274%   $246.6548   $246.65   $246.65   $246.70  
  Purchase #3 $121.83   11.139%   $135.4006   $135.40   $135.40   $135.40  
  Purchase #4 $248.85   9.751%   $273.1154   $273.12   $273.10   $273.10  
  Purchase #5 $131.65   3.438%   $136.1761   $136.18   $136.20   $136.20  
  Purchase #6 $52.69   12.449%   $59.2494   $59.25   $59.25   $59.20  
  Purchase #7 $245.35   5.341%   $258.4541   $258.45   $258.45   $258.50  
  7 purchase totals = $1,064.87       $1,159.5817   $1,159.58   $1,159.60   $1,159.60