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 $44.40   8.243%   $48.0599   $48.06   $48.05   $48.10  
  Purchase #2 $146.93   4.446%   $153.4625   $153.46   $153.45   $153.50  
  Purchase #3 $219.30   11.854%   $245.2958   $245.30   $245.30   $245.30  
  Purchase #4 $191.85   13.439%   $217.6327   $217.63   $217.65   $217.60  
  Purchase #5 $78.33   11.568%   $87.3912   $87.39   $87.40   $87.40  
  Purchase #6 $192.94   4.221%   $201.084   $201.08   $201.10   $201.10  
  Purchase #7 $153.67   13.827%   $174.918   $174.92   $174.90   $174.90  
  7 purchase totals = $1,027.42       $1,127.8441   $1,127.84   $1,127.85   $1,127.90