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 $171.97   12.543%   $193.5402   $193.54   $193.55   $193.50  
  Purchase #2 $97.27   5.575%   $102.6928   $102.69   $102.70   $102.70  
  Purchase #3 $216.87   10.766%   $240.2182   $240.22   $240.20   $240.20  
  Purchase #4 $69.50   8.745%   $75.5778   $75.58   $75.60   $75.60  
  Purchase #5 $36.95   4.553%   $38.6323   $38.63   $38.65   $38.60  
  Purchase #6 $170.41   6.398%   $181.3128   $181.31   $181.30   $181.30  
  Purchase #7 $161.53   11.193%   $179.6101   $179.61   $179.60   $179.60  
  7 purchase totals = $924.50       $1,011.5842   $1,011.58   $1,011.60   $1,011.50