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 $65.68   9.328%   $71.8066   $71.81   $71.80   $71.80  
  Purchase #2 $63.82   8.535%   $69.267   $69.27   $69.25   $69.30  
  Purchase #3 $52.28   7.330%   $56.1121   $56.11   $56.10   $56.10  
  Purchase #4 $143.31   5.833%   $151.6693   $151.67   $151.65   $151.70  
  Purchase #5 $185.36   13.825%   $210.986   $210.99   $211.00   $211.00  
  Purchase #6 $242.94   6.183%   $257.961   $257.96   $257.95   $258.00  
  Purchase #7 $5.57   4.148%   $5.801   $5.80   $5.80   $5.80  
  7 purchase totals = $758.96       $823.6030   $823.61   $823.55   $823.70