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 $47.99   12.432%   $53.9561   $53.96   $53.95   $54.00  
  Purchase #2 $231.89   9.705%   $254.3949   $254.39   $254.40   $254.40  
  Purchase #3 $61.58   11.640%   $68.7479   $68.75   $68.75   $68.70  
  Purchase #4 $71.54   7.648%   $77.0114   $77.01   $77.00   $77.00  
  Purchase #5 $154.85   5.247%   $162.975   $162.98   $163.00   $163.00  
  Purchase #6 $85.75   5.628%   $90.576   $90.58   $90.60   $90.60  
  Purchase #7 $16.96   9.679%   $18.6016   $18.60   $18.60   $18.60  
  7 purchase totals = $670.56       $726.2629   $726.27   $726.30   $726.30