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 $207.65   13.431%   $235.5395   $235.54   $235.55   $235.50  
  Purchase #2 $49.65   6.544%   $52.8991   $52.90   $52.90   $52.90  
  Purchase #3 $131.54   7.227%   $141.0464   $141.05   $141.05   $141.00  
  Purchase #4 $47.28   5.249%   $49.7617   $49.76   $49.75   $49.80  
  Purchase #5 $35.91   12.284%   $40.3212   $40.32   $40.30   $40.30  
  Purchase #6 $179.58   7.303%   $192.6947   $192.69   $192.70   $192.70  
  Purchase #7 $223.65   5.431%   $235.7964   $235.80   $235.80   $235.80  
  7 purchase totals = $875.26       $948.0590   $948.06   $948.05   $948.00