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 $228.65   13.182%   $258.7906   $258.79   $258.80   $258.80  
  Purchase #2 $171.55   4.752%   $179.7021   $179.70   $179.70   $179.70  
  Purchase #3 $96.26   8.699%   $104.6337   $104.63   $104.65   $104.60  
  Purchase #4 $169.93   12.162%   $190.5969   $190.60   $190.60   $190.60  
  Purchase #5 $38.29   12.138%   $42.9376   $42.94   $42.95   $42.90  
  Purchase #6 $235.35   11.758%   $263.0225   $263.02   $263.00   $263.00  
  Purchase #7 $199.71   11.863%   $223.4016   $223.40   $223.40   $223.40  
  7 purchase totals = $1,139.74       $1,263.0850   $1,263.08   $1,263.10   $1,263.00