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 $105.74   10.332%   $116.6651   $116.67   $116.65   $116.70  
  Purchase #2 $241.29   13.371%   $273.5529   $273.55   $273.55   $273.60  
  Purchase #3 $53.93   11.818%   $60.3034   $60.30   $60.30   $60.30  
  Purchase #4 $101.81   11.474%   $113.4917   $113.49   $113.50   $113.50  
  Purchase #5 $210.25   9.423%   $230.0619   $230.06   $230.05   $230.10  
  Purchase #6 $34.99   12.846%   $39.4848   $39.48   $39.50   $39.50  
  Purchase #7 $132.76   7.767%   $143.0715   $143.07   $143.05   $143.10  
  7 purchase totals = $880.77       $976.6313   $976.62   $976.60   $976.80