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 $66.61   11.574%   $74.3194   $74.32   $74.30   $74.30  
  Purchase #2 $120.26   11.729%   $134.3653   $134.37   $134.35   $134.40  
  Purchase #3 $62.74   11.503%   $69.957   $69.96   $69.95   $70.00  
  Purchase #4 $205.79   13.621%   $233.8207   $233.82   $233.80   $233.80  
  Purchase #5 $37.67   9.338%   $41.1876   $41.19   $41.20   $41.20  
  Purchase #6 $250.67   4.212%   $261.2282   $261.23   $261.25   $261.20  
  Purchase #7 $183.75   3.701%   $190.5506   $190.55   $190.55   $190.60  
  7 purchase totals = $927.49       $1,005.4288   $1,005.44   $1,005.40   $1,005.50