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 $151.98   7.422%   $163.26   $163.26   $163.25   $163.30  
  Purchase #2 $49.46   4.655%   $51.7624   $51.76   $51.75   $51.80  
  Purchase #3 $16.76   6.336%   $17.8219   $17.82   $17.80   $17.80  
  Purchase #4 $196.49   11.337%   $218.7661   $218.77   $218.75   $218.80  
  Purchase #5 $244.31   5.656%   $258.1282   $258.13   $258.15   $258.10  
  Purchase #6 $126.57   7.266%   $135.7666   $135.77   $135.75   $135.80  
  Purchase #7 $116.31   6.328%   $123.6701   $123.67   $123.65   $123.70  
  7 purchase totals = $901.88       $969.1753   $969.18   $969.10   $969.30