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 $47.32   9.256%   $51.6999   $51.70   $51.70   $51.70  
  Purchase #2 $185.55   9.724%   $203.5929   $203.59   $203.60   $203.60  
  Purchase #3 $142.64   3.522%   $147.6638   $147.66   $147.65   $147.70  
  Purchase #4 $226.30   10.341%   $249.7017   $249.70   $249.70   $249.70  
  Purchase #5 $121.39   3.283%   $125.3752   $125.38   $125.40   $125.40  
  Purchase #6 $194.35   5.635%   $205.3016   $205.30   $205.30   $205.30  
  Purchase #7 $75.88   5.719%   $80.2196   $80.22   $80.20   $80.20  
  7 purchase totals = $993.43       $1,063.5547   $1,063.55   $1,063.55   $1,063.60