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 $222.62   8.612%   $241.792   $241.79   $241.80   $241.80  
  Purchase #2 $19.91   12.554%   $22.4095   $22.41   $22.40   $22.40  
  Purchase #3 $53.68   9.439%   $58.7469   $58.75   $58.75   $58.70  
  Purchase #4 $228.47   9.254%   $249.6126   $249.61   $249.60   $249.60  
  Purchase #5 $58.52   7.746%   $63.053   $63.05   $63.05   $63.10  
  Purchase #6 $225.37   5.396%   $237.531   $237.53   $237.55   $237.50  
  Purchase #7 $181.30   11.671%   $202.4595   $202.46   $202.45   $202.50  
  7 purchase totals = $989.87       $1,075.6045   $1,075.60   $1,075.60   $1,075.60