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 $33.77   12.704%   $38.0601   $38.06   $38.05   $38.10  
  Purchase #2 $219.40   3.718%   $227.5573   $227.56   $227.55   $227.60  
  Purchase #3 $85.86   13.165%   $97.1635   $97.16   $97.15   $97.20  
  Purchase #4 $218.76   11.447%   $243.8015   $243.80   $243.80   $243.80  
  Purchase #5 $44.61   8.518%   $48.4099   $48.41   $48.40   $48.40  
  Purchase #6 $133.43   6.407%   $141.9789   $141.98   $142.00   $142.00  
  Purchase #7 $214.33   6.710%   $228.7115   $228.71   $228.70   $228.70  
  7 purchase totals = $950.16       $1,025.6827   $1,025.68   $1,025.65   $1,025.80