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 $35.27   11.513%   $39.3306   $39.33   $39.35   $39.30  
  Purchase #2 $245.78   6.369%   $261.4337   $261.43   $261.45   $261.40  
  Purchase #3 $44.72   5.750%   $47.2914   $47.29   $47.30   $47.30  
  Purchase #4 $70.47   4.155%   $73.398   $73.40   $73.40   $73.40  
  Purchase #5 $152.40   9.302%   $166.5762   $166.58   $166.60   $166.60  
  Purchase #6 $231.51   13.792%   $263.4399   $263.44   $263.45   $263.40  
  Purchase #7 $152.93   5.365%   $161.1347   $161.13   $161.15   $161.10  
  7 purchase totals = $933.08       $1,012.6045   $1,012.60   $1,012.70   $1,012.50