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 $67.53   12.264%   $75.8119   $75.81   $75.80   $75.80  
  Purchase #2 $158.93   4.299%   $165.7624   $165.76   $165.75   $165.80  
  Purchase #3 $217.81   6.817%   $232.6581   $232.66   $232.65   $232.70  
  Purchase #4 $230.31   13.134%   $260.5589   $260.56   $260.55   $260.60  
  Purchase #5 $67.56   6.205%   $71.7521   $71.75   $71.75   $71.80  
  Purchase #6 $230.45   13.126%   $260.6989   $260.70   $260.70   $260.70  
  Purchase #7 $250.77   7.264%   $268.9859   $268.99   $269.00   $269.00  
  7 purchase totals = $1,223.36       $1,336.2282   $1,336.23   $1,336.20   $1,336.40