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 $82.87   11.392%   $92.3106   $92.31   $92.30   $92.30  
  Purchase #2 $200.83   5.139%   $211.1507   $211.15   $211.15   $211.20  
  Purchase #3 $49.51   13.643%   $56.2646   $56.26   $56.25   $56.30  
  Purchase #4 $193.85   10.804%   $214.7936   $214.79   $214.80   $214.80  
  Purchase #5 $180.31   3.486%   $186.5956   $186.60   $186.60   $186.60  
  Purchase #6 $28.80   6.487%   $30.6683   $30.67   $30.65   $30.70  
  Purchase #7 $198.42   11.193%   $220.6292   $220.63   $220.65   $220.60  
  7 purchase totals = $934.59       $1,012.4126   $1,012.41   $1,012.40   $1,012.50