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 $233.58   8.487%   $253.4039   $253.40   $253.40   $253.40  
  Purchase #2 $154.39   9.423%   $168.9382   $168.94   $168.95   $168.90  
  Purchase #3 $56.99   3.639%   $59.0639   $59.06   $59.05   $59.10  
  Purchase #4 $237.51   4.646%   $248.5447   $248.54   $248.55   $248.50  
  Purchase #5 $121.84   13.281%   $138.0216   $138.02   $138.00   $138.00  
  Purchase #6 $106.40   3.822%   $110.4666   $110.47   $110.45   $110.50  
  Purchase #7 $31.99   9.846%   $35.1397   $35.14   $35.15   $35.10  
  7 purchase totals = $942.70       $1,013.5786   $1,013.57   $1,013.55   $1,013.50