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 $52.67   13.309%   $59.6799   $59.68   $59.70   $59.70  
  Purchase #2 $151.37   9.813%   $166.2239   $166.22   $166.20   $166.20  
  Purchase #3 $15.66   7.871%   $16.8926   $16.89   $16.90   $16.90  
  Purchase #4 $145.58   5.777%   $153.9902   $153.99   $154.00   $154.00  
  Purchase #5 $39.94   13.257%   $45.2348   $45.23   $45.25   $45.20  
  Purchase #6 $181.69   12.174%   $203.8089   $203.81   $203.80   $203.80  
  Purchase #7 $83.33   8.531%   $90.4389   $90.44   $90.45   $90.40  
  7 purchase totals = $670.24       $736.2692   $736.26   $736.30   $736.20