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 $63.49   4.827%   $66.5547   $66.55   $66.55   $66.60  
  Purchase #2 $249.77   3.322%   $258.0674   $258.07   $258.05   $258.10  
  Purchase #3 $116.25   5.592%   $122.7507   $122.75   $122.75   $122.80  
  Purchase #4 $17.49   3.284%   $18.0644   $18.06   $18.05   $18.10  
  Purchase #5 $228.49   3.422%   $236.3089   $236.31   $236.30   $236.30  
  Purchase #6 $62.84   12.452%   $70.6648   $70.66   $70.65   $70.70  
  Purchase #7 $203.81   12.420%   $229.1232   $229.12   $229.10   $229.10  
  7 purchase totals = $942.14       $1,001.5341   $1,001.52   $1,001.45   $1,001.70