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 $163.44   8.165%   $176.7849   $176.78   $176.80   $176.80  
  Purchase #2 $153.58   6.599%   $163.7147   $163.71   $163.70   $163.70  
  Purchase #3 $232.71   9.587%   $255.0199   $255.02   $255.00   $255.00  
  Purchase #4 $118.43   11.358%   $131.8813   $131.88   $131.90   $131.90  
  Purchase #5 $14.92   6.299%   $15.8598   $15.86   $15.85   $15.90  
  Purchase #6 $58.31   7.699%   $62.7993   $62.80   $62.80   $62.80  
  Purchase #7 $232.56   7.798%   $250.695   $250.70   $250.70   $250.70  
  7 purchase totals = $973.95       $1,056.7549   $1,056.75   $1,056.75   $1,056.80