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 $169.49   11.396%   $188.8051   $188.81   $188.80   $188.80  
  Purchase #2 $54.48   3.422%   $56.3443   $56.34   $56.35   $56.30  
  Purchase #3 $201.76   11.795%   $225.5576   $225.56   $225.55   $225.60  
  Purchase #4 $211.68   5.186%   $222.6577   $222.66   $222.65   $222.70  
  Purchase #5 $30.76   11.265%   $34.2251   $34.23   $34.25   $34.20  
  Purchase #6 $31.25   8.663%   $33.9572   $33.96   $33.95   $34.00  
  Purchase #7 $190.65   4.610%   $199.439   $199.44   $199.45   $199.40  
  7 purchase totals = $890.07       $960.9860   $961.00   $961.00   $961.00