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 $210.50   9.349%   $230.1796   $230.18   $230.20   $230.20  
  Purchase #2 $119.87   3.832%   $124.4634   $124.46   $124.45   $124.50  
  Purchase #3 $29.58   12.617%   $33.3121   $33.31   $33.30   $33.30  
  Purchase #4 $144.65   12.264%   $162.3899   $162.39   $162.40   $162.40  
  Purchase #5 $202.36   5.205%   $212.8928   $212.89   $212.90   $212.90  
  Purchase #6 $250.82   4.677%   $262.5509   $262.55   $262.55   $262.60  
  Purchase #7 $202.81   6.393%   $215.7756   $215.78   $215.80   $215.80  
  7 purchase totals = $1,160.59       $1,241.5643   $1,241.56   $1,241.60   $1,241.70