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 $102.41   8.844%   $111.4671   $111.47   $111.45   $111.50  
  Purchase #2 $178.67   12.795%   $201.5308   $201.53   $201.55   $201.50  
  Purchase #3 $8.52   13.405%   $9.6621   $9.66   $9.65   $9.70  
  Purchase #4 $19.56   11.710%   $21.8505   $21.85   $21.85   $21.90  
  Purchase #5 $230.84   12.159%   $258.9078   $258.91   $258.90   $258.90  
  Purchase #6 $76.38   5.281%   $80.4136   $80.41   $80.40   $80.40  
  Purchase #7 $172.70   9.221%   $188.6247   $188.62   $188.60   $188.60  
  7 purchase totals = $789.08       $872.4566   $872.45   $872.40   $872.50