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 $53.67   6.324%   $57.0641   $57.06   $57.05   $57.10  
  Purchase #2 $185.59   3.737%   $192.5255   $192.53   $192.55   $192.50  
  Purchase #3 $65.30   11.854%   $73.0407   $73.04   $73.05   $73.00  
  Purchase #4 $204.67   3.220%   $211.2604   $211.26   $211.25   $211.30  
  Purchase #5 $111.26   7.236%   $119.3108   $119.31   $119.30   $119.30  
  Purchase #6 $134.61   10.528%   $148.7817   $148.78   $148.80   $148.80  
  Purchase #7 $214.41   10.194%   $236.267   $236.27   $236.25   $236.30  
  7 purchase totals = $969.51       $1,038.2502   $1,038.25   $1,038.25   $1,038.30