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 $185.52   13.706%   $210.9474   $210.95   $210.95   $210.90  
  Purchase #2 $99.94   12.450%   $112.3825   $112.38   $112.40   $112.40  
  Purchase #3 $156.93   13.856%   $178.6742   $178.67   $178.65   $178.70  
  Purchase #4 $161.88   13.542%   $183.8018   $183.80   $183.80   $183.80  
  Purchase #5 $235.55   4.737%   $246.708   $246.71   $246.70   $246.70  
  Purchase #6 $74.69   7.416%   $80.229   $80.23   $80.25   $80.20  
  Purchase #7 $179.47   12.348%   $201.631   $201.63   $201.65   $201.60  
  7 purchase totals = $1,093.98       $1,214.3739   $1,214.37   $1,214.40   $1,214.30