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 $67.64   11.767%   $75.5992   $75.60   $75.60   $75.60  
  Purchase #2 $189.81   6.724%   $202.5728   $202.57   $202.55   $202.60  
  Purchase #3 $245.91   7.725%   $264.9065   $264.91   $264.90   $264.90  
  Purchase #4 $145.29   12.854%   $163.9656   $163.97   $163.95   $164.00  
  Purchase #5 $49.80   13.728%   $56.6365   $56.64   $56.65   $56.60  
  Purchase #6 $153.28   6.836%   $163.7582   $163.76   $163.75   $163.80  
  Purchase #7 $205.51   8.200%   $222.3618   $222.36   $222.35   $222.40  
  7 purchase totals = $1,057.24       $1,149.8006   $1,149.81   $1,149.75   $1,149.90