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 $39.30   11.339%   $43.7562   $43.76   $43.75   $43.80  
  Purchase #2 $236.49   5.208%   $248.8064   $248.81   $248.80   $248.80  
  Purchase #3 $31.86   7.590%   $34.2782   $34.28   $34.30   $34.30  
  Purchase #4 $138.86   8.219%   $150.2729   $150.27   $150.25   $150.30  
  Purchase #5 $182.60   5.109%   $191.929   $191.93   $191.95   $191.90  
  Purchase #6 $175.65   6.744%   $187.4958   $187.50   $187.50   $187.50  
  Purchase #7 $153.76   12.727%   $173.329   $173.33   $173.35   $173.30  
  7 purchase totals = $958.52       $1,029.8675   $1,029.88   $1,029.90   $1,029.90