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 $154.43   4.688%   $161.6697   $161.67   $161.65   $161.70  
  Purchase #2 $227.53   7.496%   $244.5856   $244.59   $244.60   $244.60  
  Purchase #3 $104.56   13.801%   $118.9903   $118.99   $119.00   $119.00  
  Purchase #4 $110.68   5.576%   $116.8515   $116.85   $116.85   $116.90  
  Purchase #5 $6.41   4.104%   $6.6731   $6.67   $6.65   $6.70  
  Purchase #6 $30.76   9.441%   $33.6641   $33.66   $33.65   $33.70  
  Purchase #7 $57.94   8.874%   $63.0816   $63.08   $63.10   $63.10  
  7 purchase totals = $692.31       $745.5159   $745.51   $745.50   $745.70