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 $192.66   5.782%   $203.7996   $203.80   $203.80   $203.80  
  Purchase #2 $6.76   3.741%   $7.0129   $7.01   $7.00   $7.00  
  Purchase #3 $245.26   6.795%   $261.9254   $261.93   $261.95   $261.90  
  Purchase #4 $114.33   7.613%   $123.0339   $123.03   $123.05   $123.00  
  Purchase #5 $188.43   5.807%   $199.3721   $199.37   $199.35   $199.40  
  Purchase #6 $30.73   11.483%   $34.2587   $34.26   $34.25   $34.30  
  Purchase #7 $142.39   9.611%   $156.0751   $156.08   $156.10   $156.10  
  7 purchase totals = $920.56       $985.4777   $985.48   $985.50   $985.50