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 $235.27   10.617%   $260.2486   $260.25   $260.25   $260.20  
  Purchase #2 $199.92   3.632%   $207.1811   $207.18   $207.20   $207.20  
  Purchase #3 $241.70   6.756%   $258.0293   $258.03   $258.05   $258.00  
  Purchase #4 $118.47   3.454%   $122.562   $122.56   $122.55   $122.60  
  Purchase #5 $66.81   7.622%   $71.9023   $71.90   $71.90   $71.90  
  Purchase #6 $26.50   11.604%   $29.5751   $29.58   $29.60   $29.60  
  Purchase #7 $184.39   10.689%   $204.0994   $204.10   $204.10   $204.10  
  7 purchase totals = $1,073.06       $1,153.5978   $1,153.60   $1,153.65   $1,153.60