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 $187.45   13.439%   $212.6414   $212.64   $212.65   $212.60  
  Purchase #2 $144.99   10.109%   $159.647   $159.65   $159.65   $159.60  
  Purchase #3 $111.89   5.604%   $118.1603   $118.16   $118.15   $118.20  
  Purchase #4 $188.41   4.128%   $196.1876   $196.19   $196.20   $196.20  
  Purchase #5 $56.32   12.816%   $63.538   $63.54   $63.55   $63.50  
  Purchase #6 $128.81   4.243%   $134.2754   $134.28   $134.30   $134.30  
  Purchase #7 $181.52   5.452%   $191.4165   $191.42   $191.40   $191.40  
  7 purchase totals = $999.39       $1,075.8662   $1,075.88   $1,075.90   $1,075.80